Edexcel C3 2015 June — Question 1 6 marks

Exam BoardEdexcel
ModuleC3 (Core Mathematics 3)
Year2015
SessionJune
Marks6
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicAddition & Double Angle Formulae
TypeGiven sin/cos/tan, find other expressions
DifficultyModerate -0.3 This is a straightforward application of standard trigonometric identities (double angle formula, Pythagorean identity, and compound angle formula). While it requires multiple steps and algebraic manipulation, each part follows directly from memorized formulas with no problem-solving insight needed. Slightly easier than average due to its routine nature.
Spec1.05j Trigonometric identities: tan=sin/cos and sin^2+cos^2=11.05k Further identities: sec^2=1+tan^2 and cosec^2=1+cot^21.05l Double angle formulae: and compound angle formulae

  1. Given that
$$\tan \theta ^ { \circ } = p , \text { where } p \text { is a constant, } p \neq \pm 1$$ use standard trigonometric identities, to find in terms of \(p\),
  1. \(\tan 2 \theta ^ { \circ }\)
  2. \(\cos \theta ^ { \circ }\)
  3. \(\cot ( \theta - 45 ) ^ { \circ }\) Write each answer in its simplest form.

Question 1 (part a(i)):
AnswerMarks Guidance
Answer/WorkingMark Guidance
Exponential (growth) shaped curve in any positionB1 Tolerant on slips of pen at either end
Intersections at \(\left(\ln\left(\frac{5}{2}\right), 0\right)\) and \((0, -3)\)B1 Allow \(\ln\left(\frac{5}{2}\right)\) and \(-3\) marked on correct axes; condone \((0, \ln\left(\frac{5}{2}\right))\) and \((-3,0)\); do not allow \((0.92, 0)\) unless seen elsewhere
Asymptote equation \(y = -5\)B1 Curve must appear to have asymptote at \(y=-5\); having \(-5\) marked on axis alone insufficient; extra asymptote with equation scores B0
Question 1 (part a(ii)):
AnswerMarks Guidance
Answer/WorkingMark Guidance
Correct shape or reflection of (a)(i) curve in \(x\)-axis, appearing both above and below \(x\)-axis with correct cusp curvatureB1ft Must appear both above and below \(x\)-axis
Both intersections from (a)(i) followed through, including decimalsB1ft Curve must appear both above and below \(x\)-axis
Asymptote \(y=5\) or follow-through on \(y=-C\) from (a)(i)B1ft Curve must appear to have asymptote at \(y=C\)
Question 1 (part b):
AnswerMarks Guidance
Answer/WorkingMark Guidance
\(x = \ln\left(\frac{5}{2}\right)\) or follow-through on \(x\)-intersection from part (a)B1ft Accept awrt 0.92
Question 1 (part c):
AnswerMarks Guidance
Answer/WorkingMark Guidance
\(2e^x - 5 = -2\) or \(-2e^x + 5 = 2 \Rightarrow x = \ln(\ldots)\)M1 Allow squaring: \((2e^x-5)^2=4 \Rightarrow e^x=\ldots \Rightarrow x=\ln(\ldots), \ln(\ldots)\)
\(x = \ln\left(\frac{3}{2}\right)\) or exact equivalent e.g. \(x=\ln 1.5\)A1 Decimal answer awrt 0.405
\(x = \ln\left(\frac{7}{2}\right)\) or exact equivalent e.g. \(x=\ln 3.5\)B1 Decimal answer awrt 1.25
If both answers given in decimals only with no working, \(x \approx 1.25, 0.405\)SC 100
# Question 1 (part a(i)):

| Answer/Working | Mark | Guidance |
|---|---|---|
| Exponential (growth) shaped curve in any position | B1 | Tolerant on slips of pen at either end |
| Intersections at $\left(\ln\left(\frac{5}{2}\right), 0\right)$ and $(0, -3)$ | B1 | Allow $\ln\left(\frac{5}{2}\right)$ and $-3$ marked on correct axes; condone $(0, \ln\left(\frac{5}{2}\right))$ and $(-3,0)$; do not allow $(0.92, 0)$ unless seen elsewhere |
| Asymptote equation $y = -5$ | B1 | Curve must appear to have asymptote at $y=-5$; having $-5$ marked on axis alone insufficient; extra asymptote with equation scores B0 |

# Question 1 (part a(ii)):

| Answer/Working | Mark | Guidance |
|---|---|---|
| Correct shape or reflection of (a)(i) curve in $x$-axis, appearing both above and below $x$-axis with correct cusp curvature | B1ft | Must appear both above and below $x$-axis |
| Both intersections from (a)(i) followed through, including decimals | B1ft | Curve must appear both above and below $x$-axis |
| Asymptote $y=5$ or follow-through on $y=-C$ from (a)(i) | B1ft | Curve must appear to have asymptote at $y=C$ |

# Question 1 (part b):

| Answer/Working | Mark | Guidance |
|---|---|---|
| $x = \ln\left(\frac{5}{2}\right)$ or follow-through on $x$-intersection from part (a) | B1ft | Accept awrt 0.92 |

# Question 1 (part c):

| Answer/Working | Mark | Guidance |
|---|---|---|
| $2e^x - 5 = -2$ or $-2e^x + 5 = 2 \Rightarrow x = \ln(\ldots)$ | M1 | Allow squaring: $(2e^x-5)^2=4 \Rightarrow e^x=\ldots \Rightarrow x=\ln(\ldots), \ln(\ldots)$ |
| $x = \ln\left(\frac{3}{2}\right)$ or exact equivalent e.g. $x=\ln 1.5$ | A1 | Decimal answer awrt 0.405 |
| $x = \ln\left(\frac{7}{2}\right)$ or exact equivalent e.g. $x=\ln 3.5$ | B1 | Decimal answer awrt 1.25 |
| If both answers given in decimals only with no working, $x \approx 1.25, 0.405$ | SC 100 | |

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\begin{enumerate}
  \item Given that
\end{enumerate}

$$\tan \theta ^ { \circ } = p , \text { where } p \text { is a constant, } p \neq \pm 1$$

use standard trigonometric identities, to find in terms of $p$,\\
(a) $\tan 2 \theta ^ { \circ }$\\
(b) $\cos \theta ^ { \circ }$\\
(c) $\cot ( \theta - 45 ) ^ { \circ }$

Write each answer in its simplest form.\\

\hfill \mbox{\textit{Edexcel C3 2015 Q1 [6]}}