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Application of Derivatives — Maths STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceMathsApplication of Derivatives1 Mark
MCQ
The function $f(x)=k x$ - $\sin x$ is strictly increasing for
  • A
    k > 1
  • B
    k < 1
  • C
    k > -1
  • D
    k < -1
✓

Answer

Given, $f(x)=k x-\sin x$
$
\begin{array}{l}
\Rightarrow f^{\prime}(x)=k-\cos x>0 \quad(\because f(x) \text { is strictly increasing } \therefore f(x)>0) \\
\Rightarrow k>\cos x \\
\therefore k>1 \quad(\because \cos x \in[-1,1])
\end{array}
$

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