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Need solution for rd sharma maths class 12 chapter 16 Increasing and Decreasing functions exercise Multiple choice question, question 21

Answers (1)

Correct option (c)

Hint: If f(x)  is increasing function {f}'(x)\geq 0

Given: f(x)=\cos |x|-2 a x+b

Explanation:It is given that

f(x)=\cos |x|-2 a x+b …..(i)

Differentiate (i) w.r.t  x

f^{\prime}(x)=-\sin x+2 a 

\because f(x) is increasing function, {f}'(x)\geq 0

\begin{aligned} &\Rightarrow-\sin x+2 a \geq 0 \\ &\Rightarrow \sin x \geq 2 a \end{aligned} 

\because Minimum value \sin x of is -1

\therefore \frac{-1}{2} \geq a 

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