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Figure 2 shows a sketch of the curve C with parametric equations $x = 5t^2 - 4$, y = (9 - t^2)$ The curve C cuts the x-axis at the points A and B - Edexcel - A-Level Maths Pure - Question 1 - 2010 - Paper 7

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Question 1

Figure-2-shows-a-sketch-of-the-curve-C-with-parametric-equations--$x-=-5t^2---4$,---y-=-(9---t^2)$--The-curve-C-cuts-the-x-axis-at-the-points-A-and-B-Edexcel-A-Level Maths Pure-Question 1-2010-Paper 7.png

Figure 2 shows a sketch of the curve C with parametric equations $x = 5t^2 - 4$, y = (9 - t^2)$ The curve C cuts the x-axis at the points A and B. (a) Find the ... show full transcript

Worked Solution & Example Answer:Figure 2 shows a sketch of the curve C with parametric equations $x = 5t^2 - 4$, y = (9 - t^2)$ The curve C cuts the x-axis at the points A and B - Edexcel - A-Level Maths Pure - Question 1 - 2010 - Paper 7

Step 1

Find the x-coordinate at the point A and the x-coordinate at the point B.

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Answer

To find the x-coordinates where the curve cuts the x-axis, we set y = 0:

9t2=09 - t^2 = 0

This simplifies to:

t2=9t^2 = 9

Thus, we find:

t=3 or t=3t = 3 \text{ or } t = -3

Next, we substitute these values back into the equation for x:

For t=3t = 3:

x=5(3)24=5(9)4=454=41x = 5(3)^2 - 4 = 5(9) - 4 = 45 - 4 = 41

For t=3t = -3:

x=5(3)24=5(9)4=454=41x = 5(-3)^2 - 4 = 5(9) - 4 = 45 - 4 = 41

For t=0t = 0:

x=5(0)24=04=4x = 5(0)^2 - 4 = 0 - 4 = -4

Thus, the x-coordinates are:

  • At point A: x=4x = -4
  • At point B: x=41x = 41

Step 2

Use integration to find the area of R.

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Answer

To find the area of region R, we will integrate the function defined by the parametric equations. We know:

dydx=dy/dtdx/dt\frac{dy}{dx} = \frac{dy/dt}{dx/dt}

First, we calculate:

dydt=2t\frac{dy}{dt} = -2t

dxdt=10t\frac{dx}{dt} = 10t

Then we find:

dydx=2t10t=15\frac{dy}{dx} = \frac{-2t}{10t} = -\frac{1}{5}

To find the area, we can use the formula:

A=abydxdtdtA = \int_{a}^{b} y \frac{dx}{dt} dt

Here, y=9t2y = 9 - t^2 and the limits of integration will be from 3-3 to 33:

A=33(9t2)10dtA = \int_{-3}^{3} (9 - t^2) \cdot 10 dt

This simplifies to:

A=1033(9t2)dtA = 10 \int_{-3}^{3} (9 - t^2) dt

Calculating the definite integral, we evaluate:

(9t2)dt=9tt33\int (9 - t^2) dt = 9t - \frac{t^3}{3}

Thus, compute from -3 to 3:

A=10[(9(3)(3)33)(9(3)(3)33)]A = 10 [ (9(3) - \frac{(3)^3}{3}) - (9(-3) - \frac{(-3)^3}{3})]

Calculating this gives us:

A=10[(279)(27+9)]=10[18+18]=1036=360 units2A = 10 [ (27 - 9) - (-27 + 9) ] = 10 [ 18 + 18 ] = 10 \cdot 36 = 360 \text{ units}^2

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