Question

The length of longest interval in which f(x) = 3sin x – 4 sin³x is increasing –

• A. $\frac{\pi}{2}$
• B. $\frac{\pi}{3}$
• C. $\frac{\pi}{6}$
• D. None of these

Answer 1

Answer: (B)

$\frac{\pi}{3}$

Answer 2

f(x) = sin 3x ­ Ž $\frac{–\pi}{2}$ £ 3x £$\frac{\pi}{2}$ Ž $\frac{–\pi}{6}$ £ x $\frac{\pi}{6}$

Ž length of longest interval = $\frac{\pi}{3}$.