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
Question 8
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+2x3
Now, we apply the power rule to differentiate:
dxdy=4x3+6x2.
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)=0.
This gives:
(x = 0)
(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.
At (x = 0):
dxdy=4(0)3+6(0)2=0
At (x = -2):
dxdy=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:
For the x-intercepts:
0=(x−k2)(x−k+2)
This gives intercepts at (x = k^2) and (x = k - 2).
For the y-intercept, set (x = 0):
y=(0−k2)(0−k+2)=k2(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.