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Derivatives & Second-Order Derivatives · Question 84 of 96

Question 84

EasyOriginal question

If y=x3y = x^{3} and x2d2ydx2=kyx^{2}\frac{d^2y}{dx^2} = ky, what is kk?

Options for question 84

Show the answer and explanation
CorrectNot quiteAnswer C

Correct answer: C

Explanation

  1. dydx=3x2\frac{dy}{dx} = 3x^{2} and d2ydx2=6x\frac{d^2y}{dx^2} = 6x.

  2. x2⋅6x=6x3=6yx^{2} \cdot 6x = 6x^{3} = 6y, so k=6k = 6.

Worth noting

3 comes from the first derivative: xdydx=3yx\frac{dy}{dx} = 3y.

Concept
A constant from a second derivative
Typical time
60 s
Your time
—
The rule this testsEquations with second derivatives
Practise this chapter →

Ten questions from Derivatives & Second-Order Derivatives, at your own pace.

Practise this chapter →

Ten questions from Derivatives & Second-Order Derivatives, at your own pace.