2026 NORTHBROOKS P2 Q6

2026 NORTHBROOKS P2 Q6

Secondary 4
10 marks
  1. Complete the table of values for \(y=\dfrac{x^3}{4}-3x+2\).
    Values are given to one decimal place where appropriate.
    \(x\)−4−3−2−101234
    \(y\)−24.364.82−0.8−26
    [1]
  2. On the grid, draw the graph of \(y=\dfrac{x^3}{4}-3x+2\) for \(-4\leq x\leq4\).[3]
  3. By drawing a tangent, find the gradient of the curve at \(x=-1\).[1]
  4. The equation \(\dfrac{x^3}{4}-3x=k\) has two solutions.
    Use your graph to find the two possible values of \(k\).[2]
  5. By drawing a suitable straight line on the grid, solve the inequality \(x^3-16x-4>0\).[3]

Solution:

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Answer:(a) \(-0.3\). (b) Smooth cubic through table points. (c) About \(-2.25\). (d) \(k=4\) or \(-4\). (e) Within the drawn domain, about \(-3.9<x<-0.25\); globally also \(x>4.1196\ldots\).

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