Taylor series

148 questions · 31 question types identified

Evaluate limit using series

A question is this type if and only if it asks to find a limit as x→0 or x→∞ using series expansions or l'Hôpital's rule.

10
6.8% of questions
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13 Use l'Hôpital's rule to prove that $$\lim _ { x \rightarrow \pi } \left( \frac { x \sin 2 x } { \cos \left( \frac { x } { 2 } \right) } \right) = - 4 \pi$$
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Explicit differential equation series solution

The differential equation is given in explicit form dy/dx = f(x,y) or d²y/dx² = f(x,y,dy/dx), and successive derivatives are found by direct differentiation and substitution.

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5.4% of questions
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4. $$\frac { \mathrm { d } ^ { 2 } y } { \mathrm {~d} x ^ { 2 } } + y \frac { \mathrm {~d} y } { \mathrm {~d} x } = x , \quad y = 0 , \frac { \mathrm {~d} y } { \mathrm {~d} x } = 2 \text { at } x = 1$$ Find a series solution of the differential equation in ascending powers of ( \(x - 1\) ) up to and including the term in \(( x - 1 ) ^ { 3 }\).
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Direct multiplication of series

Questions that require multiplying two known Maclaurin series directly (e.g., e^x cos x, (1+x) sin x, e^x ln(1+3x), sin x sin 2x sin 4x).

8
5.4% of questions
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1 Find the first three non-zero terms of the Maclaurin series for $$( 1 + x ) \sin x$$ simplifying the coefficients.
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Maclaurin series for ln(trigonometric expressions)

Finding Maclaurin series for logarithmic functions involving trigonometric expressions such as ln(cos x), ln(cos ax), ln(sin x + cos x), ln(1 + sin x), or ln(1 + tan x). These require using trigonometric derivatives and often involve finding non-zero terms.

8
5.4% of questions
Direct substitution into standard series

Questions that ask to write down or find a Maclaurin series by directly substituting an expression (like x², 2x, or x³) into a single standard series (e^x, ln(1+x), sin x, cos x, etc.).

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4.7% of questions
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2
  1. Given that \(\mathrm { f } ( x ) = \sin \left( 2 x + \frac { 1 } { 4 } \pi \right)\), show that \(\mathrm { f } ( x ) = \frac { 1 } { 2 } \sqrt { 2 } ( \sin 2 x + \cos 2 x )\).
  2. Hence find the first four terms of the Maclaurin series for \(\mathrm { f } ( x )\). [You may use appropriate results given in the List of Formulae.]
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Find series for logarithmic function

A question is this type if and only if it asks for a series expansion of a logarithmic function (ln of some expression) by differentiation or standard results.

6
4.1% of questions
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2 Find the Maclaurin's series for \(\ln \cosh x\) up to and including the term in \(x ^ { 4 }\).
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Deduce related series from given series

A question is this type if and only if it asks to write down or deduce a series for a related function (e.g., ln(1-x) from ln(1+x)) without full derivation.

6
4.1% of questions
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3
  1. Find the first three terms of the Maclaurin series for \(\ln ( 2 + x )\).
  2. Write down the first three terms of the series for \(\ln ( 2 - x )\), and hence show that, if \(x\) is small, then $$\ln \left( \frac { 2 + x } { 2 - x } \right) \approx x$$
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Maclaurin series for composite exponential/root functions

Questions asking to find Maclaurin series by differentiation for functions involving roots or exponentials of trigonometric/exponential expressions, such as √(a+e^x), √(a+sin x), or e^(sin x).

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4.1% of questions
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3. $$y = \sqrt { 8 + \mathrm { e } ^ { x } } , \quad x \in \mathbb { R }$$ Find the series expansion for \(y\) in ascending powers of \(x\), up to and including the term in \(x ^ { 2 }\), giving each coefficient in its simplest form.
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Implicit differential equation series solution

The differential equation is given in implicit form (e.g., y·d²y/dx² + (dy/dx)² + y = 0 or (1+x²)·d²y/dx² + x·dy/dx = y), requiring algebraic manipulation to find successive derivatives.

6
4.1% of questions
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5. $$y \frac { \mathrm {~d} ^ { 2 } y } { \mathrm {~d} x ^ { 2 } } + 3 x \frac { \mathrm {~d} y } { \mathrm {~d} x } - 3 y ^ { 2 } = 0$$ Given that at \(x = 0 , y = 2\) and \(\frac { \mathrm { d } y } { \mathrm {~d} x } = 1\)
  1. show that, at \(x = 0 , \frac { \mathrm {~d} ^ { 3 } y } { \mathrm {~d} x ^ { 3 } } = \frac { 3 } { 2 }\)
  2. Find a series solution for \(y\) up to and including the term in \(x ^ { 3 }\)
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Taylor series about π/4

Questions asking for Taylor series expansion about x = π/4, typically involving tan x, sec²x, or cos 2x.

6
4.1% of questions
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5. (a) Find the Taylor expansion of \(\cos 2 x\) in ascending powers of \(\left( x - \frac { \pi } { 4 } \right)\) up to and including the term in \(\left( x - \frac { \pi } { 4 } \right) ^ { 5 }\).
(b) Use your answer to (a) to obtain an estimate of \(\cos 2\), giving your answer to 6 decimal places.
(3)(Total 8 marks)
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Maclaurin series for ln(a+bx)

Finding Maclaurin series for logarithmic functions of the form ln(a+bx) or ln(1/(1-bx)) using differentiation. These are straightforward applications where successive derivatives follow a clear pattern.

6
4.1% of questions
Use series to find error or validity

A question is this type if and only if it asks about the error in a series approximation, percentage error, or range of validity of a series.

5
3.4% of questions
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15 The expression given in line 34 is used to calculate \(\sum _ { r = 1 } ^ { 6 } \frac { 1 } { r }\).
Show that the error in the result is less than \(1.5 \%\) of the true value.
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Match series to function form

A question is this type if and only if it gives partial series information and asks which function or what constants match that series.

5
3.4% of questions
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3 Which of the following functions has the fourth term \(- \frac { 1 } { 720 } x ^ { 6 }\) in its Maclaurin series expansion? Circle your answer.
[0pt] [1 mark]
\(\sin x\)
\(\cos x\)
\(\mathrm { e } ^ { x }\)
\(\ln ( 1 + x )\)
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Exponential or trigonometric base functions

Questions where the base function is exponential, trigonometric, or their products (e.g., e^x sin x, e^(cos²x), tan²x), requiring standard differentiation rules to establish the derivative relationship.

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3.4% of questions
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2 It is given that \(y = 2 ^ { x }\).
  1. By differentiating \(\ln y\) with respect to \(x\), show that \(\frac { \mathrm { dy } } { \mathrm { dx } } = 2 ^ { \mathrm { x } } \ln 2\).
  2. Write down \(\frac { d ^ { 2 } y } { d x ^ { 2 } }\).
  3. Hence find the first three terms in the Maclaurin's series for \(2 ^ { X }\).
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Inverse functions (inverse trig/hyperbolic)

Questions where the base function is an inverse trigonometric or inverse hyperbolic function (e.g., tan⁻¹(2x), sin⁻¹(2x), sech⁻¹(x+1/2), tanh⁻¹(x)), requiring implicit differentiation or chain rule with inverse function derivatives.

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3.4% of questions
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2
  1. Given that $$f ( x ) = \tan ^ { - 1 } ( x + 1 )$$ find \(f ( 0 )\) and \(f ^ { \prime } ( 0 )\), and show that \(f ^ { \prime \prime } ( 0 ) = - \frac { 1 } { 2 }\).
  2. Hence find the first three terms in the Maclaurin series for \(f ( x )\)
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Taylor series about π/3 or π/6

Questions asking for Taylor series expansion about x = π/3 or x = π/6, typically involving sin, cos, tan, sec, or cot functions.

5
3.4% of questions
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4. $$f ( x ) = \sin \left( \frac { 3 } { 2 } x \right)$$
  1. Find the Taylor series expansion for \(\mathrm { f } ( x )\) about \(\frac { \pi } { 3 }\) in ascending powers of \(\left( x - \frac { \pi } { 3 } \right)\) up to and including the term in \(\left( x - \frac { \pi } { 3 } \right) ^ { 4 }\)
  2. Hence obtain an estimate of \(\sin \frac { 1 } { 2 }\), giving your answer to 4 decimal places.
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Use series to approximate integral

A question is this type if and only if it asks to use a series expansion to find an approximate value for a definite integral.

4
2.7% of questions
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1
  1. Find the Maclaurin series for \(\sin ^ { - 1 } x\) up to and including the term in \(x ^ { 3 }\).
  2. Deduce an approximation to \(\int _ { 0 } ^ { \frac { 1 } { 5 } } \frac { 1 } { \sqrt { 1 - u ^ { 2 } } } \mathrm {~d} u\), giving your answer as a fraction.
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Hyperbolic power functions

Questions involving hyperbolic functions raised to powers (e.g., cosh^n x, sinh x sin x) where the derivative relationship involves recurrence relations or products of hyperbolic and trigonometric functions.

4
2.7% of questions
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5. $$y = \sin x \sinh x$$
  1. Show that \(\frac { \mathrm { d } ^ { 4 } y } { \mathrm {~d} x ^ { 4 } } = - 4 y\)
  2. Hence find the first three non-zero terms of the Maclaurin series for \(y\), giving each coefficient in its simplest form.
  3. Find an expression for the \(n\)th non-zero term of the Maclaurin series for \(y\).
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Maclaurin series of shifted function

A question is this type if and only if it asks for a Maclaurin series (expansion about x = 0) of a function that has been horizontally shifted, such as f(x + a).

4
2.7% of questions
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1 Find the Maclaurin's series for \(\tan \left( x + \frac { 1 } { 4 } \pi \right)\) up to and including the term in \(x ^ { 2 }\).
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Composition of two standard series

Questions that require substituting one Maclaurin series into another standard series (e.g., e^(e^x - 1), ln(1 + sin x), cosh(ix)) involving nested functions.

4
2.7% of questions
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2 It is given that \(\mathrm { f } ( x ) = \ln ( 1 + \sin x )\). Using standard series, find the Maclaurin series for \(\mathrm { f } ( x )\) up to and including the term in \(x ^ { 3 }\).
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Combining or manipulating standard series

Questions that require adding, subtracting, or using algebraic identities to combine multiple standard series or derive one series from another (e.g., finding cos²x from cos 2x, finding sin²x from cos 2x, or adding e^(1+x²) + e^(1-x)).

4
2.7% of questions
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2 Find the Maclaurin's series for \(\mathrm { e } ^ { 1 + x ^ { 2 } } + \mathrm { e } ^ { 1 - x }\) up to and including the term in \(x ^ { 2 }\).
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Maclaurin series for ln(exponential expressions)

Finding Maclaurin series for logarithmic functions involving exponential expressions such as ln(e^x + c), ln(e^(ax) cos x), or ln(1 + e^x). These often involve simplifying using logarithm properties and may combine exponential and trigonometric derivatives.

4
2.7% of questions
Use series to approximate numerical value

A question is this type if and only if it asks to substitute a specific value into a series to approximate a number (not an integral).

3
2.0% of questions
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4. (a) (i) Given that \(f ( x ) = \sqrt { 1 + 2 x }\), find \(f ^ { \prime } ( x )\) and \(f ^ { \prime \prime } ( x )\).
(ii) Hence, find the first three terms of the Maclaurin series for \(\sqrt { 1 + 2 x }\).
(b) Hence, using a suitable value for \(x\), show that \(\sqrt { 5 } \approx \frac { 143 } { 64 }\).
[0pt] [BLANK PAGE]
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Use binomial with exponential series

A question is this type if and only if it requires combining a binomial expansion with an exponential series to find terms of a product.

3
2.0% of questions
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2
  1. Write down the expansion of \(\mathrm { e } ^ { 3 x }\) in ascending powers of \(x\) up to and including the term in \(x ^ { 2 }\).
  2. Hence, or otherwise, find the term in \(x ^ { 2 }\) in the expansion, in ascending powers of \(x\), of \(\mathrm { e } ^ { 3 x } ( 1 + 2 x ) ^ { - \frac { 3 } { 2 } }\).
    (4 marks)
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Maclaurin series for inverse trigonometric functions

Questions asking to find Maclaurin series by differentiation for inverse trigonometric functions such as arcsin(x), arctan(x), or arccos(x).

3
2.0% of questions
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3. $$f ( x ) = \arcsin x \quad - 1 \leqslant x \leqslant 1$$
  1. Determine the first two non-zero terms, in ascending powers of \(x\), of the Maclaurin series for \(\mathrm { f } ( x )\), giving each coefficient in its simplest form.
  2. Substitute \(x = \frac { 1 } { 2 }\) into the answer to part (a) and hence find an approximate value for \(\pi\) Give your answer in the form \(\frac { p } { q }\) where \(p\) and \(q\) are integers to be determined.
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Taylor series about x = 1

A question is this type if and only if it asks for a Taylor series expansion about the point x = 1, typically involving logarithmic or algebraic functions.

3
2.0% of questions
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5. $$y = \sqrt { 4 + \ln x } \quad x > \frac { 1 } { 2 }$$
  1. Show that $$\frac { \mathrm { d } ^ { 2 } y } { \mathrm {~d} x ^ { 2 } } = - \frac { 9 + 2 \ln x } { 4 x ^ { 2 } ( 4 + \ln x ) ^ { \frac { 3 } { 2 } } }$$
  2. Hence, or otherwise, determine the Taylor series expansion about \(x = 1\) for \(y\), in ascending powers of ( \(x - 1\) ), up to and including the term in \(( x - 1 ) ^ { 2 }\), giving each coefficient in simplest form.
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Maclaurin series for hyperbolic inverse functions

Questions asking to find Maclaurin series by differentiation for inverse hyperbolic functions such as tanh^(-1)(x).

2
1.4% of questions
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2 It is given that \(\mathrm { f } ( x ) = \tanh ^ { - 1 } x\).
  1. Show that \(\mathrm { f } ^ { \prime \prime \prime } ( x ) = \frac { 2 \left( 1 + 3 x ^ { 2 } \right) } { \left( 1 - x ^ { 2 } \right) ^ { 3 } }\).
  2. Hence find the Maclaurin series for \(\mathrm { f } ( x )\), up to and including the term in \(x ^ { 3 }\).
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Maclaurin series for products/secant

Questions asking to find Maclaurin series by differentiation for products like e^x·tan(x) or sec(x) where the function structure requires product/quotient rule techniques.

2
1.4% of questions
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8
  1. The function f is defined as \(\mathrm { f } ( x ) = \sec x\) 8
    1. Show that \(\mathrm { f } ^ { ( 4 ) } ( 0 ) = 5\)
      8
  2. (ii) Hence find the first three non-zero terms of the Maclaurin series for \(\mathrm { f } ( x ) = \sec x\)
    8
  3. Prove that $$\lim _ { x \rightarrow 0 } \left( \frac { \sec x - \cosh x } { x ^ { 4 } } \right) = \frac { 1 } { 6 }$$
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Differential equation given

Questions that provide a differential equation relating derivatives (e.g., (x²+1)y'' = 2y² + (1-2x)y') and ask to derive higher-order relationships by differentiating the equation itself, then find the series.

2
1.4% of questions
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9. $$\left( x ^ { 2 } + 1 \right) \frac { \mathrm { d } ^ { 2 } y } { \mathrm {~d} x ^ { 2 } } = 2 y ^ { 2 } + ( 1 - 2 x ) \frac { \mathrm { d } y } { \mathrm {~d} x }$$
  1. By differentiating equation (I) with respect to \(x\), show that $$\left( x ^ { 2 } + 1 \right) \frac { \mathrm { d } ^ { 3 } y } { \mathrm {~d} x ^ { 3 } } = ( 1 - 4 x ) \frac { \mathrm { d } ^ { 2 } y } { \mathrm {~d} x ^ { 2 } } + ( 4 y - 2 ) \frac { \mathrm { d } y } { \mathrm {~d} x }$$ Given that \(y = 1\) and \(\frac { \mathrm { d } y } { \mathrm {~d} x } = 1\) at \(x = 0\),
  2. find the series solution for \(y\), in ascending powers of \(x\), up to and including the term in \(x _ { 3 }\).(4)
  3. Use your series to estimate the value of \(y\) at \(x = - 0.5\), giving your answer to two decimal places.(1)
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Series for reciprocal functions

Questions that require finding the series for 1/f(x) by multiplying the reciprocal series with the original series to get 1 (e.g., sec x from cos x).

2
1.4% of questions
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7
    1. Write down the first three terms of the binomial expansion of \(( 1 + y ) ^ { - 1 }\), in ascending powers of \(y\).
    2. By using the expansion $$\cos x = 1 - \frac { x ^ { 2 } } { 2 ! } + \frac { x ^ { 4 } } { 4 ! } - \ldots$$ and your answer to part (a)(i), or otherwise, show that the first three non-zero terms in the expansion, in ascending powers of \(x\), of \(\sec x\) are $$1 + \frac { x ^ { 2 } } { 2 } + \frac { 5 x ^ { 4 } } { 24 }$$
  1. By using Maclaurin's theorem, or otherwise, show that the first two non-zero terms in the expansion, in ascending powers of \(x\), of \(\tan x\) are $$x + \frac { x ^ { 3 } } { 3 }$$
  2. Hence find \(\lim _ { x \rightarrow 0 } \left( \frac { x \tan 2 x } { \sec x - 1 } \right)\).
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Series for composite expressions

Questions that require finding series for functions of series, such as (ln(1+x))^2 or ln(e^(2x) + e^(-2x)), where the outer function must be applied to an inner series.

2
1.4% of questions
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1
  1. Write down and simplify the first three terms of the Maclaurin series for \(\mathrm { e } ^ { 2 x }\).
  2. Hence show that the Maclaurin series for $$\ln \left( \mathrm { e } ^ { 2 x } + \mathrm { e } ^ { - 2 x } \right)$$ begins \(\ln a + b x ^ { 2 }\), where \(a\) and \(b\) are constants to be found.
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