Question

The length of a longest interval in which the function 3 sin x – 4 sin³x is increasing, is

• A. $\frac{\pi}{3}$
• B. $\frac{\pi}{2}$
• C. $\frac{3\pi}{2}$
• D. p

Answer 1

Answer: (A)

$\frac{\pi}{3}$

Answer 2

f(x) = sin3x

f ¢(x) = 3cos3x > 0

̃ cos3x > 0

̃ –$\frac{\pi}{2}$ < 3x < $\frac{\pi}{2}$

̃ – $\frac{\pi}{6}$< x < $\frac{\pi}{6}$