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Figure 2 shows a sketch of part of the curve C with equation y = x³ - 10x² + kx, where k is a constant - Edexcel - A-Level Maths Pure - Question 9 - 2010 - Paper 3

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Figure-2-shows-a-sketch-of-part-of-the-curve-C-with-equation--y-=-x³---10x²-+-kx,-where-k-is-a-constant-Edexcel-A-Level Maths Pure-Question 9-2010-Paper 3.png

Figure 2 shows a sketch of part of the curve C with equation y = x³ - 10x² + kx, where k is a constant. The point P on C is the maximum turning point. Given that ... show full transcript

Worked Solution & Example Answer:Figure 2 shows a sketch of part of the curve C with equation y = x³ - 10x² + kx, where k is a constant - Edexcel - A-Level Maths Pure - Question 9 - 2010 - Paper 3

Step 1

(a) show that k = 28

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Answer

To show that k = 28, we first need to differentiate the given curve equation:

dydx=3x220x+k.\frac{dy}{dx} = 3x^2 - 20x + k.

At the maximum turning point P, where x = 2, the derivative must equal zero:

dydx=03(2)220(2)+k=0.\frac{dy}{dx} = 0 \Rightarrow 3(2)^2 - 20(2) + k = 0.

Calculating this gives:

1240+k=012 - 40 + k = 0

This simplifies to:

k28=0k=28.k - 28 = 0 \Rightarrow k = 28.

Step 2

(b) Use calculus to find the exact area of R

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Answer

To find the area of region R, we will integrate the curve from x = 0 to x = 2 (the x-coordinate of point P).

First, substitute k = 28 into the curve equation:

y = x³ - 10x² + 28x.

Next, we compute the definite integral:

02(x310x2+28x)dx.\int_0^2 (x^3 - 10x^2 + 28x) \, dx.

This can be evaluated as follows:

  1. Find the antiderivative:

    (x310x2+28x)dx=x4410x33+14x2+C.\int (x^3 - 10x^2 + 28x) \, dx = \frac{x^4}{4} - \frac{10x^3}{3} + 14x^2 + C.

  2. Evaluate from 0 to 2:

    \left[ \frac{(2)^4}{4} - \frac{10(2)^3}{3} + 14(2)^2 \right] - \left[ \frac(0)^4}{4} - \frac{10(0)^3}{3} + 14(0)^2 \right]

Calculating the values:

=[4803+56]0=4+56803=60803=180803=1003.= \left[ 4 - \frac{80}{3} + 56 \right] - 0 = 4 + 56 - \frac{80}{3} = 60 - \frac{80}{3} = \frac{180 - 80}{3} = \frac{100}{3}.

Therefore, the exact area of region R is:

1003\frac{100}{3}.

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