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Figure 4 shows a sketch of the curve C with equation $$ y = 5x^2 - 9x + 11, \, x \geq 0 $$ The point P with coordinates (4, 15) lies on C - Edexcel - A-Level Maths Pure - Question 16 - 2017 - Paper 2

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Figure-4-shows-a-sketch-of-the-curve-C-with-equation--$$-y-=-5x^2---9x-+-11,-\,-x-\geq-0-$$--The-point-P-with-coordinates-(4,-15)-lies-on-C-Edexcel-A-Level Maths Pure-Question 16-2017-Paper 2.png

Figure 4 shows a sketch of the curve C with equation $$ y = 5x^2 - 9x + 11, \, x \geq 0 $$ The point P with coordinates (4, 15) lies on C. The line l is the tange... show full transcript

Worked Solution & Example Answer:Figure 4 shows a sketch of the curve C with equation $$ y = 5x^2 - 9x + 11, \, x \geq 0 $$ The point P with coordinates (4, 15) lies on C - Edexcel - A-Level Maths Pure - Question 16 - 2017 - Paper 2

Step 1

Differentiate the curve C

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Answer

First, we start by differentiating the function to find the gradient of the curve at point P.

dydx=10x9\frac{dy}{dx} = 10x - 9

At point P where x=4x = 4:

dydxx=4=10(4)9=31\frac{dy}{dx}\bigg|_{x=4} = 10(4) - 9 = 31

Step 2

Equation of the tangent line l

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Answer

Using the point-slope form of the line, we can find the equation of the tangent line at point P (4, 15):

y15=31(x4)y - 15 = 31(x - 4)

This simplifies to:

y=31x109y = 31x - 109

Step 3

Set up the integral for the area R

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Answer

The area R can be determined by the integral of the difference between the curve C and the tangent line l from the y-axis to where they intersect. We first find the intersection points:

Set the equations equal:

5x29x+11=31x1095x^2 - 9x + 11 = 31x - 109

Rearranging gives us:

5x240x+120=05x^2 - 40x + 120 = 0

This simplifies to:

x28x+24=0x^2 - 8x + 24 = 0

Using the quadratic formula:

x=8±(8)24(1)(24)2(1)x = \frac{8 \pm \sqrt{(-8)^2 - 4(1)(24)}}{2(1)}

We find out the limits of integration are from x = 0 to x = 4.

Step 4

Calculate the area R

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Answer

Now we compute the area R:

AreaR=04((5x29x+11)(31x109))dxArea \, R = \int_0^4 \left( (5x^2 - 9x + 11) - (31x - 109) \right) \, dx

This becomes:

04(5x240x+120)dx\int_0^4 \left( 5x^2 - 40x + 120 \right) \, dx

Calculating the integral:

=[53x320x2+120x]04= \left[ \frac{5}{3}x^3 - 20x^2 + 120x \right]_0^4

Evaluating this from 0 to 4 gives:

=(53(64)20(16)+480)0= \left( \frac{5}{3}(64) - 20(16) + 480 \right) - 0

Calculating:

=(3203320+480)=3203+480320=320+480×39603=320+14409603=8003=24= \left( \frac{320}{3} - 320 + 480 \right) = \frac{320}{3} + 480 - 320 = \frac{320 + 480\times 3 - 960}{3} = \frac{320 + 1440 - 960}{3} = \frac{800}{3} = 24

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