Convert Cartesian to polar equation

5

1. Show that the curve with Cartesian equation $$x ^ { 2 } - y ^ { 2 } = a$$ where \(a\) is a positive constant, has polar equation \(r ^ { 2 } = a \sec 2 \theta\).
   The curve \(C\) has polar equation \(r ^ { 2 } = \operatorname { asec } 2 \theta\), where \(a\) is a positive constant, for \(0 \leqslant \theta < \frac { 1 } { 4 } \pi\).
2. Sketch \(C\) and state the minimum distance of \(C\) from the pole.
3. Find, in terms of \(a\), the exact value of the area of the region enclosed by \(C\), the initial line, and the half-line \(\theta = \frac { 1 } { 12 } \pi\). [You may use any result from the list of formulae (MF19) without proof.] [4]

7

1. Show that the curve with Cartesian equation $$\left( x ^ { 2 } + y ^ { 2 } \right) ^ { \frac { 5 } { 2 } } = 4 x y \left( x ^ { 2 } - y ^ { 2 } \right)$$ has polar equation \(r = \sin 4 \theta\).
   The curve \(C\) has polar equation \(r = \sin 4 \theta\), for \(0 \leqslant \theta \leqslant \frac { 1 } { 4 } \pi\).
2. Sketch \(C\) and state the equation of the line of symmetry.
3. Find the exact value of the area of the region enclosed by \(C\).
4. Using the identity \(\sin 4 \theta \equiv 4 \sin \theta \cos ^ { 3 } \theta - 4 \sin ^ { 3 } \theta \cos \theta\), find the maximum distance of \(C\) from the line \(\theta = \frac { 1 } { 2 } \pi\). Give your answer correct to 2 decimal places.
   If you use the following lined page to complete the answer(s) to any question(s), the question number(s) must be clearly shown.

6

1. Show that the curve with Cartesian equation $$\left( x ^ { 2 } + y ^ { 2 } \right) ^ { 2 } = 36 \left( x ^ { 2 } - y ^ { 2 } \right)$$ has polar equation \(r ^ { 2 } = 36 \cos 2 \theta\).
   The curve \(C\) has polar equation \(r ^ { 2 } = 36 \cos 2 \theta\), for \(- \frac { 1 } { 4 } \pi \leqslant \theta \leqslant \frac { 1 } { 4 } \pi\).
2. Sketch \(C\) and state the maximum distance of a point on \(C\) from the pole.
3. Find the area of the region enclosed by \(C\).
4. Find the maximum distance of a point on \(C\) from the initial line, giving the answer in exact form.

6 A curve \(C\) has polar equation $$r ^ { 2 } \sin 2 \theta = 8$$

1. Find the cartesian equation of \(C\) in the form \(y = \mathrm { f } ( x )\).
2. Sketch the curve \(C\).
3. The line with polar equation \(r = 2 \sec \theta\) intersects \(C\) at the point \(A\). Find the polar coordinates of \(A\).

3 A curve \(C\) has polar equation \(r ( 1 + \cos \theta ) = 2\).

1. Find the cartesian equation of \(C\), giving your answer in the form \(y ^ { 2 } = \mathrm { f } ( x )\).
2. The straight line with polar equation \(4 r = 3 \sec \theta\) intersects the curve \(C\) at the points \(P\) and \(Q\). Find the length of \(P Q\).

3

1. Show that \(x ^ { 2 } = 1 - 2 y\) can be written in the form \(x ^ { 2 } + y ^ { 2 } = ( 1 - y ) ^ { 2 }\).
2. A curve has cartesian equation \(x ^ { 2 } = 1 - 2 y\). Find its polar equation in the form \(r = \mathrm { f } ( \theta )\), given that \(r > 0\).

3 The diagram shows a sketch of a circle which passes through the origin \(O\). \includegraphics[max width=\textwidth, alt={}, center]{13cfb9ca-9495-4b69-80c5-9fb7e8e0f957-3_423_451_356_794} The equation of the circle is \(( x - 3 ) ^ { 2 } + ( y - 4 ) ^ { 2 } = 25\) and \(O A\) is a diameter.

1. Find the cartesian coordinates of the point \(A\).
2. Using \(O\) as the pole and the positive \(x\)-axis as the initial line, the polar coordinates of \(A\) are \(( k , \alpha )\).
   1. Find the value of \(k\) and the value of \(\tan \alpha\).
   2. Find the polar equation of the circle \(( x - 3 ) ^ { 2 } + ( y - 4 ) ^ { 2 } = 25\), giving your answer in the form \(r = p \cos \theta + q \sin \theta\).

8

1. A curve has cartesian equation \(x y = 8\). Show that the polar equation of the curve is \(r ^ { 2 } = 16 \operatorname { cosec } 2 \theta\).
2. The diagram shows a sketch of the curve, \(C\), whose polar equation is $$r ^ { 2 } = 16 \operatorname { cosec } 2 \theta , \quad 0 < \theta < \frac { \pi } { 2 }$$ \includegraphics[max width=\textwidth, alt={}, center]{c4bce668-61f1-4be0-97ee-c635df7e1fc6-4_364_567_1635_726}
   1. Find the polar coordinates of the point \(N\) which lies on the curve \(C\) and is closest to the pole \(O\).
   2. The circle whose polar equation is \(r = 4 \sqrt { 2 }\) intersects the curve \(C\) at the points \(P\) and \(Q\). Find, in an exact form, the polar coordinates of \(P\) and \(Q\).
   3. The obtuse angle \(P N Q\) is \(\alpha\) radians. Find the value of \(\alpha\), giving your answer to three significant figures.
      (5 marks)

2 The Cartesian equation of a circle is \(( x + 8 ) ^ { 2 } + ( y - 6 ) ^ { 2 } = 100\).
Using the origin \(O\) as the pole and the positive \(x\)-axis as the initial line, find the polar equation of this circle, giving your answer in the form \(r = p \sin \theta + q \cos \theta\).
(4 marks)

3 A curve has polar equation \(r ( 4 - 3 \cos \theta ) = 4\). Find its Cartesian equation in the form \(y ^ { 2 } = \mathrm { f } ( x )\).
[0pt] [4 marks]

4

1. The curve with Cartesian equation \(\frac { x ^ { 2 } } { c } + \frac { y ^ { 2 } } { d } = 1\) is mapped onto the curve with polar equation \(r = \frac { 10 } { 3 - 2 \cos \theta }\) by a single geometrical transformation. By writing the polar equation as a Cartesian equation in a suitable form, find the values of the constants \(c\) and \(d\).
2. Hence describe the geometrical transformation referred to in part (a).
   [0pt] [1 mark]

11 A point has Cartesian coordinates \(( x , y )\) and polar coordinates \(( r , \theta )\) where \(r \geq 0\) and \(- \pi < \theta \leq \pi\) 11

1. Express \(r\) in terms of \(x\) and \(y\) 11
2. Express \(x\) in terms of \(r\) and \(\theta\) 11
3. The curve \(C _ { 1 }\) has the polar equation $$r ( 2 + \cos \theta ) = 1 \quad - \pi < \theta \leq \pi$$ 11 (c) (i) Show that the Cartesian equation of \(C _ { 1 }\) can be written as $$a y ^ { 2 } = ( 1 + b x ) ( 1 + x )$$ where \(a\) and \(b\) are integers to be determined.
   11 (c) (ii) The curve \(C _ { 2 }\) has the Cartesian equation $$a x ^ { 2 } = ( 1 + b y ) ( 1 + y )$$ where \(a\) and \(b\) take the same values as in part (c)(i). Describe fully a single transformation that maps the curve \(C _ { 1 }\) onto the curve \(C _ { 2 }\)

11 A curve has cartesian equation \(x ^ { 3 } + y ^ { 3 } = 2 x y\). \(C\) is the portion of the curve for which \(x \geqslant 0\) and \(y \geqslant 0\). The equation of \(C\) in polar form is given by \(r = \mathrm { f } ( \theta )\) for \(0 \leqslant \theta \leqslant \frac { 1 } { 2 } \pi\).

1. Find \(f ( \theta )\).
2. Find an expression for \(\mathrm { f } \left( \frac { 1 } { 2 } \pi - \theta \right)\), giving your answer in terms of \(\sin \theta\) and \(\cos \theta\).
3. Hence find the line of symmetry of \(C\).
4. Find the value of \(r\) when \(\theta = \frac { 1 } { 4 } \pi\).
5. By finding values of \(\theta\) when \(r = 0\), show that \(C\) has a loop.

9 A function is defined by \(y = f ( t )\) where \(f ( t ) = \ln ( 1 + a t )\) and \(a\) is a constant.

1. By considering \(\frac { d y } { d t } , \frac { d ^ { 2 } y } { d t ^ { 2 } } , \frac { d ^ { 3 } y } { d t ^ { 3 } }\) and \(\frac { d ^ { 4 } y } { d t ^ { 4 } }\), make a conjecture for a general formula for \(\frac { d ^ { n } y } { d t ^ { n } }\) in terms of \(n\) and \(a\) for any integer \(n \geqslant 1\).
2. Use induction to prove the formula conjectured in part (a).
3. In the case where \(\mathrm { f } ( t ) = \ln ( 1 + 2 t )\), find the rate at which the \(6 ^ { \text {th } }\) derivative of \(\mathrm { f } ( t )\) is varying when \(t = \frac { 3 } { 2 }\).

1

1. A family of curves is given by the equation $$x ^ { 2 } + y ^ { 2 } + 2 a x y = 1 ( * )$$ where the parameter \(a\) is a real number.
   You may find it helpful to use a slider (for \(a\) ) to investigate this family of curves.
   1. On the axes in the Printed Answer Booklet, sketch the curve in each of the cases
      • \(a = 0\)
      • \(a = 0.5\)
      • \(a = 2\)
      • State a feature of the curve for the cases \(a = 0 , a = 0.5\) that is not a feature of the curve in the case \(a = 2\).
      • In the case \(a = 1\), the curve consists of two straight lines. Determine the equations of these lines.
      • 1. Find an equation of the curve (*) in polar form.
        2. Hence, or otherwise, find, in exact form, the area bounded by the curve, the positive part of the \(x\)-axis and the positive part of the \(y\)-axis, in the case \(a = 2\).
2. In this part of the question \(m\) is any real number.
Describing all possible cases, determine the pairs of values \(a\) and \(m\) for which the curve with equation (*) intersects the straight line given by \(y = m x\).

2 A curve has polar equation \(r ( 1 - \sin \theta ) = 4\). Find its cartesian equation in the form \(y = \mathrm { f } ( x )\).

7 A curve has cartesian equation \(x ^ { 3 } + y ^ { 3 } = 2 x y\). \(C\) is the portion of the curve for which \(x \geqslant 0\) and \(y \geqslant 0\). The equation of \(C\) in polar form is given by \(r = \mathrm { f } ( \theta )\) for \(0 \leqslant \theta \leqslant \frac { 1 } { 2 } \pi\).

1. Find \(f ( \theta )\).
2. Find an expression for \(\mathrm { f } \left( \frac { 1 } { 2 } \pi - \theta \right)\), giving your answer in terms of \(\sin \theta\) and \(\cos \theta\).
3. Hence find the line of symmetry of \(C\).
4. Find the value of \(r\) when \(\theta = \frac { 1 } { 4 } \pi\).
5. By finding values of \(\theta\) when \(r = 0\), show that \(C\) has a loop.

Point \(P\) has polar coordinates \(\left(2, \frac{2\pi}{3}\right)\). Which of the following are the Cartesian coordinates of \(P\)? Circle your answer. [1 mark] \((1, -\sqrt{3})\) \quad \((-\sqrt{3}, 1)\) \quad \((\sqrt{3}, -1)\) \quad \((-1, \sqrt{3})\)