Q243 / 270 · NDA 2019 (Phase 2) · Mathematics

Paragraph: Let $f(x)=x^2+2 x-5$ and $g(x)=5 x+30$
Question: If $h(x)=5 f(x)-x g(x)$, then what is the derivative of $h(x)$ ?

  • A
    -40
  • Correct answer
    B
    -20
  • C
    -10
  • D
    0

Solution

$\begin{aligned} & \text { } h(x)=5 f(x)-x g(x) \\ & =5\left[x^2+2 x-5\right]-x[5 x+30] \\ & =-20 x-25 \\ & \therefore \quad h^{\prime}(x)=-20\end{aligned}$

Hence, the correct answer is option: 'B'.

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