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The curve $C_1$ has equation $$y = x^2(x + 2)$$ (a) Find \( \frac{dy}{dx} \) - Edexcel - A-Level Maths Pure - Question 10 - 2012 - Paper 1

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The curve $C_1$ has equation $$y = x^2(x + 2)$$ (a) Find \( \frac{dy}{dx} \). (b) Sketch $C_1$, showing the coordinates of the points where $C_1$ meets the x-axis... show full transcript

Worked Solution & Example Answer:The curve $C_1$ has equation $$y = x^2(x + 2)$$ (a) Find \( \frac{dy}{dx} \) - Edexcel - A-Level Maths Pure - Question 10 - 2012 - Paper 1

Step 1

Find \( \frac{dy}{dx} \)

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Answer

To find ( \frac{dy}{dx} ), we first multiply out the expression:

y=x3+2x2y = x^3 + 2x^2

Now, differentiating with respect to x:

dydx=3x2+4x\frac{dy}{dx} = 3x^2 + 4x

Step 2

Sketch $C_1$, showing the coordinates of the points where $C_1$ meets the x-axis.

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Answer

To find the points where the curve meets the x-axis, we set (y = 0):

0=x2(x+2)0 = x^2 (x + 2)

This gives:

  1. (x = 0)
  2. (x = -2)

These points are where the curve intersects the x-axis: (0,0) and (-2,0). The sketch should show these points as intersections.

Step 3

Find the gradient of $C_1$ at each point where $C_1$ meets the x-axis.

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Answer

To find the gradient at the x-axis intersection points, we will evaluate (\frac{dy}{dx}) at the points x = 0 and x = -2:

  1. At (x = 0):

dydxx=0=3(0)2+4(0)=0\frac{dy}{dx} \bigg|_{x=0} = 3(0)^2 + 4(0) = 0

  1. At (x = -2):

dydxx=2=3(2)2+4(2)=128=4\frac{dy}{dx} \bigg|_{x=-2} = 3(-2)^2 + 4(-2) = 12 - 8 = 4

Thus, the gradients are 0 and 4 at (0,0) and (-2,0) respectively.

Step 4

Sketch $C_2$, showing the coordinates of the points where $C_2$ meets the x and y axes.

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Answer

To find where C2C_2 meets the x-axis, we set y=0y = 0:

0=(xk2)(xk+2)0 = (x-k^2)(x-k+2)

This gives:

  1. (x = k^2)
  2. (x = k - 2)

To find where C2C_2 meets the y-axis, we set (x=0):

y=(0k2)(0k+2)=k2(k2)y = (0-k^2)(0-k+2) = k^2(k-2)

In the sketch, mark these intersections accordingly.

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