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In Figure 2 the curve C has equation $y = 6x - x^2$ and the line L has equation $y = 2x$ - Edexcel - A-Level Maths Pure - Question 9 - 2008 - Paper 2

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In Figure 2 the curve C has equation $y = 6x - x^2$ and the line L has equation $y = 2x$. (a) Show that the curve C intersects the x-axis at $x = 0$ and $x = 6$. (... show full transcript

Worked Solution & Example Answer:In Figure 2 the curve C has equation $y = 6x - x^2$ and the line L has equation $y = 2x$ - Edexcel - A-Level Maths Pure - Question 9 - 2008 - Paper 2

Step 1

Show that the curve C intersects the x-axis at $x = 0$ and $x = 6$

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Answer

To find the points where the curve C intersects the x-axis, we set y=0y = 0 for the equation of the curve:

0=6xx20 = 6x - x^2

Rearranging gives:

x26x=0x^2 - 6x = 0

Factoring yields:

x(x6)=0x(x - 6) = 0

Thus, the solutions are:

x=0andx=6.x = 0 \quad \text{and} \quad x = 6.

Therefore, the curve C intersects the x-axis at the points (0,0)(0, 0) and (6,0)(6, 0).

Step 2

Show that the line L intersects the curve C at the points $(0, 0)$ and $(4, 8)$

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Answer

To find the intersection points, we set the equations equal to each other:

6xx2=2x6x - x^2 = 2x

Rearranging gives:

x24x=0x^2 - 4x = 0

Factoring yields:

x(x4)=0x(x - 4) = 0

Thus, the solutions are:

x=0andx=4.x = 0 \quad \text{and} \quad x = 4.

For x=0x = 0, substituting back into the line equation:

y=2(0)=0(0,0).y = 2(0) = 0 \rightarrow (0, 0).

For x=4x = 4:

y=2(4)=8(4,8).y = 2(4) = 8 \rightarrow (4, 8).

The line L intersects the curve C at the points (0,0)(0, 0) and (4,8)(4, 8).

Step 3

Use calculus to find the area of R

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Answer

To find the area R between the curve C and the line L, we need to calculate the integral of the top function minus the bottom function from x=0x = 0 to x=4x = 4:

Area=04(6xx22x)dx=04(4xx2)dx.\text{Area} = \int_0^4 (6x - x^2 - 2x) \, dx = \int_0^4 (4x - x^2) \, dx.

Calculating the integral:

=[2x2x33]04=(2(4)2(4)33)(2(0)2(0)33)=(32643)=96643=323.= \left[ 2x^2 - \frac{x^3}{3} \right]_0^4 = \left( 2(4)^2 - \frac{(4)^3}{3} \right) - \left( 2(0)^2 - \frac{(0)^3}{3} \right) = \left( 32 - \frac{64}{3} \right) = \frac{96 - 64}{3} = \frac{32}{3}.

Therefore, the area of region R is:

323 square units.\frac{32}{3} \text{ square units}.

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