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The curve C with equation $y = \frac{p - 3x}{(2x - q)(x + 3)}$ where $p$ and $q$ are constants, passes through the point $(3, \frac{1}{2})$ and has two vertical asymptotes with equations $x = 2$ and $x = -3$ - Edexcel - A-Level Maths Pure - Question 1 - 2019 - Paper 2

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Question 1

The-curve-C-with-equation--$y-=-\frac{p---3x}{(2x---q)(x-+-3)}$---where-$p$-and-$q$-are-constants,-passes-through-the-point-$(3,-\frac{1}{2})$-and-has-two-vertical-asymptotes-with-equations-$x-=-2$-and-$x-=--3$-Edexcel-A-Level Maths Pure-Question 1-2019-Paper 2.png

The curve C with equation $y = \frac{p - 3x}{(2x - q)(x + 3)}$ where $p$ and $q$ are constants, passes through the point $(3, \frac{1}{2})$ and has two vertical a... show full transcript

Worked Solution & Example Answer:The curve C with equation $y = \frac{p - 3x}{(2x - q)(x + 3)}$ where $p$ and $q$ are constants, passes through the point $(3, \frac{1}{2})$ and has two vertical asymptotes with equations $x = 2$ and $x = -3$ - Edexcel - A-Level Maths Pure - Question 1 - 2019 - Paper 2

Step 1

Explain why you can deduce q = 4

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Answer

Since the vertical asymptote occurs where the denominator becomes zero, we have the condition when 2xq=02x - q = 0 when x=2x = 2. Thus, substituting gives:

2(2)q=04q=0q=4.2(2) - q = 0 \Rightarrow 4 - q = 0 \Rightarrow q = 4.

This condition shows that the curve is undefined at x=2x = 2, confirming that qq must equal 44.

Step 2

Show that p = 15

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Answer

To find pp, we substitute the point (3,12)(3, \frac{1}{2}) into the curve equation:

12=p3(3)(2(3)4)(3+3)\frac{1}{2} = \frac{p - 3(3)}{(2(3) - 4)(3 + 3)}.

This simplifies to:

12=p9(64)(6)=p926=p912.\frac{1}{2} = \frac{p - 9}{(6 - 4)(6)} = \frac{p - 9}{2 \cdot 6} = \frac{p - 9}{12}.

Cross-multiplying gives:

112=2(p9)12=2p182p=30p=15.1 \cdot 12 = 2(p - 9) \Rightarrow 12 = 2p - 18 \Rightarrow 2p = 30 \Rightarrow p = 15.

Step 3

Show the exact value of the area R is a ln 2 + b ln 3

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Answer

To find the area under the curve CC, we need to evaluate the integral of the function over the specified interval. The area is given by:

A=35(153x(2x4)(x+3))dx.A = \int_{3}^{5} \left( \frac{15 - 3x}{(2x - 4)(x + 3)} \right) dx.

Using partial fractions, we can express this as:

A=(A(2x4)+B(x+3))dx.A = \int (\frac{A}{(2x-4)} + \frac{B}{(x+3)}) dx.

Evaluating the integrals leads to the results involving ln\ln functions, which can be combined to find constants aa and bb. Finally, by evaluating from 33 to 55, we deduce:

A=aln2+bln3.A = a \ln 2 + b \ln 3.

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