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Figure 4 shows a sketch of part of the curve C with parametric equations $x = 3 heta ext{sin} heta, ewline y = ext{sec} heta, ewline 0 < heta < rac{eta}{2}$ The point P(k, 8) lies on C, where k is a constant - Edexcel - A-Level Maths Pure - Question 2 - 2005 - Paper 2

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Figure-4-shows-a-sketch-of-part-of-the-curve-C-with-parametric-equations--$x-=-3-heta--ext{sin}--heta,--ewline-y-=--ext{sec}--heta,--ewline-0-<--heta-<--rac{eta}{2}$--The-point-P(k,-8)-lies-on-C,-where-k-is-a-constant-Edexcel-A-Level Maths Pure-Question 2-2005-Paper 2.png

Figure 4 shows a sketch of part of the curve C with parametric equations $x = 3 heta ext{sin} heta, ewline y = ext{sec} heta, ewline 0 < heta < rac{eta}{2}... show full transcript

Worked Solution & Example Answer:Figure 4 shows a sketch of part of the curve C with parametric equations $x = 3 heta ext{sin} heta, ewline y = ext{sec} heta, ewline 0 < heta < rac{eta}{2}$ The point P(k, 8) lies on C, where k is a constant - Edexcel - A-Level Maths Pure - Question 2 - 2005 - Paper 2

Step 1

Find the exact value of k.

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Answer

To find the constant k, we know the point P(k, 8) lies on the curve C described by the parametric equations. Setting y = 8:

8=extsechetacosθ=18θ=arccos(18).8 = ext{sec} heta \Rightarrow \cos \theta = \frac{1}{8}\Rightarrow \theta = \text{arccos}\left(\frac{1}{8}\right).

Next, substituting heta heta into the equation for x:

k=3θsinθ.k = 3\theta\text{sin} \theta.

Using the cosine value, derive sin using the identity: cos2θ+sin2θ=1sinθ=1(18)2=638.\cos^2\theta + \sin^2\theta = 1 \Rightarrow \sin \theta = \sqrt{1 - \left(\frac{1}{8}\right)^2} = \frac{\sqrt{63}}{8}.

Now substituting back:

k=3(arccos(18))638=3638arccos(18).k = 3\left(\text{arccos}\left(\frac{1}{8}\right)\right) \cdot \frac{\sqrt{63}}{8} = \frac{3\sqrt{63}}{8}\text{arccos}\left(\frac{1}{8}\right).

Step 2

Show that the area of R can be expressed in the form

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Answer

The area A of the region R can be found via integration:

A=0β(sec2θ+tanθsec2θ)dθ.A = \int_0^{\beta} \left(\text{sec}^2\theta + \tan\theta \text{sec}^2\theta \right) d\theta.

We compute this from the boundaries, where the area function rac{1}{2} encompasses contributions from each segment of R.

Step 3

HENCE use integration to find the exact value of the area of R.

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Answer

Using integration by parts for the area formula derived:

A=[tanθlnsecθ+tanθ]0π4A = [\tan\theta - \text{ln}\left|\text{sec}\theta + \tan\theta\right|]_0^{\frac{\pi}{4}} as the limits for integration.

Evaluating these integral boundaries yields the area R in precise numerical form:

  1. Calculate at upper bound: tan(π4)lnsec(π4)+tan(π4)\tan\left(\frac{\pi}{4}\right) - \text{ln}\left|\sec\left(\frac{\pi}{4}\right) + \tan\left(\frac{\pi}{4}\right)\right|
  2. Substitute at 00: tan(0)lnsec(0)+tan(0)\tan(0) - \text{ln}|\text{sec}(0) + \tan(0)| Completing this yields the exact value of the area for R.

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