Question 1

Paper 2, calculatorMedium6 marks

The function ff is defined, for x∈Rx\in\mathbb R by

f(x)=14x4−32x2+2x.f(x)=\frac14x^4-\frac32x^2+2x.

Figure 1 shows the graph of f′(x)=(x+2)(x−1)2f'(x)=(x+2)(x-1)^2 for −3≤x≤3-3\leq x\leq 3

-3-2-1123-18-16-14-12-10-8-6-4-20246810121416182022xf'(x)
(a)

Use Figure 1 to state the xx-coordinates of the stationary points of ff and classify each as a local maximum, a local minimum or neither. Justify your classifications using the sign of f′(x)f'(x) on either side.

[3]
(b)

Use Figure 1 to determine the xx-coordinates of the points of inflexion of ff Hence determine the coordinates of both points of inflexion and the gradient of ff at each.

[3]

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