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1.9.17 Concavity and the second derivative (A-level only)

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Question 45

The curve C has equation y=f(x),x>0y = f(x), x > 0y=f(x),x>0.

Given that

  • the point P(1,12)P(1, 12)P(1,12) lies on CCC
  • f′(x)=6x+kx3f'(x) = 6\sqrt{x} + \frac{k}{x^3}f′(x)=6x​+x3k​ where kkk is a constant
  • f′′(x)=0f''(x) = 0f′′(x)=0 at PPP
a.

Find the exact value of kkk.

[4]
b.

Find f(x)f(x)f(x), giving your answer in simplest form.

[4]

1.9.17 Concavity and the second derivative (A-level only) Questions

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