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JAMB 2015 · UTME · Q34

Find ddxcos⁡(3x2−2x)\dfrac{d}{dx}\cos(3x^2 - 2x).

Worked solution (try it first)
  1. Chain rule: cos⁡u\cos u differentiates to −sin⁡u-\sin u times dudx\frac{du}{dx}.
  2. Here u=3x2−2xu = 3x^2 - 2x, so dudx=6x−2\frac{du}{dx} = 6x - 2.
  3. So the derivative is −(6x−2)sin⁡(3x2−2x)-(6x - 2)\sin(3x^2 - 2x), option D.

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