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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 2 - 2019 - Paper 1

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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 2-2019-Paper 1.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 asym... 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 2 - 2019 - Paper 1

Step 1

Explain why you can deduce $q = 4$

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Answer

Given the equation of the curve, the vertical asymptotes occur when the denominator equals zero.

For the asymptote at x=2x = 2, we have:
2(2)q=02(2) - q = 0.
This leads to:
4q=04 - q = 0,
therefore, q=4q = 4.
This indicates that for any value of xx approaching 2, the function approaches infinity, confirming x=2x = 2 as a vertical asymptote.

Step 2

Show that $p = 15$

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Answer

To find pp, substitute the point (3,12)(3, \frac{1}{2}) into the curve's equation.
Setting y=12y = \frac{1}{2} when x=3x = 3, we have:
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)\frac{1}{2} = \frac{p - 9}{(6 - 4)(6)}
12=p926\frac{1}{2} = \frac{p - 9}{2 \cdot 6}
Multiplying both sides by 1212 results in:
6=p96 = p - 9
Thus, solving for pp gives:
p = 15.

Step 3

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

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Answer

To find the area of region RR, set up the integral bounded by the curve and the line x=3x = 3.
This is expressed as: Area=03ydx=03p3x(2x4)(x+3)dx\text{Area} = \int_{0}^{3} y \, dx = \int_{0}^{3} \frac{p - 3x}{(2x - 4)(x + 3)} \, dx Substituting p=15p = 15 gives: 03153x(2x4)(x+3)dx\int_{0}^{3} \frac{15 - 3x}{(2x - 4)(x + 3)} \, dx. Use partial fractions to decompose the integrand which leads to finding constants AA and BB, so: 153x(2x4)(x+3)=A2x4+Bx+3\frac{15 - 3x}{(2x - 4)(x + 3)} = \frac{A}{2x - 4} + \frac{B}{x + 3}. By solving for AA and BB, proceed to evaluate the integral from 00 to 33, leading to the exact area in the form of aln2+bln3a \ln 2 + b \ln 3.

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