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Figure 3 shows a sketch of part of the curve C with equation $y = x(x + 4)(x - 2)$ The curve C crosses the x-axis at the origin O and at the points A and B - Edexcel - A-Level Maths Pure - Question 8 - 2013 - Paper 4

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Question 8

Figure-3-shows-a-sketch-of-part-of-the-curve-C-with-equation--$y-=-x(x-+-4)(x---2)$--The-curve-C-crosses-the-x-axis-at-the-origin-O-and-at-the-points-A-and-B-Edexcel-A-Level Maths Pure-Question 8-2013-Paper 4.png

Figure 3 shows a sketch of part of the curve C with equation $y = x(x + 4)(x - 2)$ The curve C crosses the x-axis at the origin O and at the points A and B. (a) W... show full transcript

Worked Solution & Example Answer:Figure 3 shows a sketch of part of the curve C with equation $y = x(x + 4)(x - 2)$ The curve C crosses the x-axis at the origin O and at the points A and B - Edexcel - A-Level Maths Pure - Question 8 - 2013 - Paper 4

Step 1

Use integration to find the total area of the finite region shown shaded in Figure 3.

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Answer

To find the area of the finite region, we will integrate the function from the left intersection point A to the right intersection point B. Hence, the area can be expressed as:

Area=42(x(x+4)(x2))dxArea = \int_{-4}^{2} (x(x + 4)(x - 2)) \, dx

Expanding the integrand:

=42(x3+2x28x)dx= \int_{-4}^{2} (x^3 + 2x^2 - 8x) \, dx

Now we integrate term by term:

=[x44+2x334x2]42= \left[ \frac{x^4}{4} + \frac{2x^3}{3} - 4x^2 \right]_{-4}^{2}

Calculating at the bounds:

At x=2x = 2: =244+2(23)34(22)=4+16316=416+163=12+163=363+163=203= \frac{2^4}{4} + \frac{2(2^3)}{3} - 4(2^2) = 4 + \frac{16}{3} - 16 = 4 - 16 + \frac{16}{3} = -12 + \frac{16}{3} = -\frac{36}{3} + \frac{16}{3} = -\frac{20}{3}

At x=4x = -4: =(4)44+2(4)334(4)2=64128364=1283= \frac{(-4)^4}{4} + \frac{2(-4)^3}{3} - 4(-4)^2 = 64 - \frac{128}{3} - 64 = -\frac{128}{3}

Now subtract the two results:

So,

Area=(203(1283))=(203+1283)=1083=36Area = \left(-\frac{20}{3} - (-\frac{128}{3})\right) = \left(-\frac{20}{3} + \frac{128}{3}\right) = \frac{108}{3} = 36

Thus, the total area of the region is 36 square units.

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