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# Solution for Function F(X) = Cos X − 2 λ X is Monotonic Decreasing When (A) λ > 1/2 (B) λ < 1/2 (C) λ < 2 (D) λ > 2 - CBSE (Commerce) Class 12 - Mathematics

ConceptIncreasing and Decreasing Functions

#### Question

Function f(x) = cos x − 2 λ x is monotonic decreasing when
(a) λ > 1/2
(b) λ < 1/2
(c) λ < 2
(d) λ > 2

#### Solution

$f\left( x \right) = \cos x - 2 \lambda x$

$f'\left( x \right) = - \sin x - 2 \lambda$

$\text { For f(x) to be decreasing, we must have }$

$f'\left( x \right) < 0$

$\Rightarrow - \sin x - 2 \lambda < 0$

$\Rightarrow sin x + 2 \lambda > 0$

$\Rightarrow 2 \lambda > - \sin x$

$\text { We know that the maximum value of -sin x is 1 }.$

$\Rightarrow 2 \lambda > 1$

$\Rightarrow \lambda > \frac{1}{2}$

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#### Video TutorialsVIEW ALL [3]

Solution Function F(X) = Cos X − 2 λ X is Monotonic Decreasing When (A) λ > 1/2 (B) λ < 1/2 (C) λ < 2 (D) λ > 2 Concept: Increasing and Decreasing Functions.
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