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The curve C₁ has equation $$y = x^3(x + 2)$$ (a) Find \(\frac{dy}{dx}\) - Edexcel - A-Level Maths Pure - Question 8 - 2012 - Paper 1

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The curve C₁ has equation $$y = x^3(x + 2)$$ (a) Find \(\frac{dy}{dx}\). (b) Sketch C₁, showing the coordinates of the points where C₁ meets the x-axis. (c) Find... show full transcript

Worked Solution & Example Answer:The curve C₁ has equation $$y = x^3(x + 2)$$ (a) Find \(\frac{dy}{dx}\) - Edexcel - A-Level Maths Pure - Question 8 - 2012 - Paper 1

Step 1

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

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Answer

To find (\frac{dy}{dx}), we first expand the equation:

y=x3(x+2)=x4+2x3y = x^3(x + 2) = x^4 + 2x^3

Now, we apply the power rule to differentiate:

dydx=4x3+6x2\frac{dy}{dx} = 4x^3 + 6x^2.

Step 2

Sketch C₁, showing the coordinates of the points where C₁ meets the x-axis

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Answer

To find where C₁ meets the x-axis, we set (y = 0):

x3(x+2)=0x^3(x + 2) = 0.

This gives:

  1. (x = 0)
  2. (x + 2 = 0 \Rightarrow x = -2)

Therefore, C₁ meets the x-axis at the points ((0, 0)) and ((-2, 0)). The sketch should indicate that the curve intersects the x-axis at these points, with appropriate curvature.

Step 3

Find the gradient of C₁ at each point where C₁ meets the x-axis

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Answer

We have already calculated (\frac{dy}{dx} = 4x^3 + 6x^2). Now, let’s evaluate the gradient at the x-intercepts.

  1. At (x = 0): dydx=4(0)3+6(0)2=0\frac{dy}{dx} = 4(0)^3 + 6(0)^2 = 0

  2. At (x = -2): dydx=4(2)3+6(2)2=4(8)+6(4)=32+24=8\frac{dy}{dx} = 4(-2)^3 + 6(-2)^2 = 4(-8) + 6(4) = -32 + 24 = -8

Thus, the gradients of C₁ at the points ((0, 0)) and ((-2, 0)) are 0 and -8 respectively.

Step 4

Sketch C₂, showing the coordinates of the points where C₂ meets the x and y axes

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Answer

To find the points where C₂ meets the axes, we will set (y = 0) and evaluate:

  1. For the x-intercepts: 0=(xk2)(xk+2)0 = (x - k^2)(x - k + 2) This gives intercepts at (x = k^2) and (x = k - 2).

  2. For the y-intercept, set (x = 0): y=(0k2)(0k+2)=k2(k2)y = (0 - k^2)(0 - k + 2) = k^2(k - 2) Therefore, the coordinates of where C₂ meets the axes should be noted as ((k^2, 0)) and ((k - 2, 0)) and ((0, k^2(k - 2))). The sketch should reflect a horizontal translation.

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