Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Applications of Derivatives

Question:

Match List I with List II

LIST I LIST II
A. sin 2 x I. decreases from 1 to 0 in $\left(0, \frac{\pi}{2}\right)$
B. tan x II. decreases if $x \in \left(0, \frac{\pi}{6}\right)$
C. cos x III. increases from 0 to 1 in $\left(0, \frac{\pi}{4}\right)$
D. cos 3 x IV. is an increasing function in each quadrant

Choose the correct answer from the options given below :

Options:

A-III, B-II, C-IV, D-I

A-III, B-IV, C-I, D-II

A-I, B-II, C-III, D-IV

A-IV, B-I, C-II, D-III

Correct Answer:

A-III, B-IV, C-I, D-II

Explanation:

The correct answer is Option (2) → A-III, B-IV, C-I, D-II

(A) $y=\sin 2x$

$y'=2\cos 2x=0$

$x=\frac{π}{4}$

so $\sin 2x$ increases from 0 → 1 in $(0,\frac{π}{4})$ (III)

(B) $y=\tan x$

$y'=\sec^2x=0⇒x=\frac{π}{2}$

but $\sec^2x≥0$ always of $\tan x$ increasing in each quadrant (IV)

(C) $y=\cos x$

$y'=-\sin x=0⇒x=0,π,2π,....$

$⇒\cos x$ is decreasing from 1 to 0 in $(0,\frac{π}{6})$ (I)

(D) $y=\cos 3x$

= $\cos z$ decreasing in $z∈(0,\frac{π}{2})$

$⇒x∈(0,\frac{π}{6})$ (II)