Q. Solution of the inequality $\sin^{4}{\left( \frac{x}{3} \right) + \cos^{4}{\left( \frac{x}{3} \right) > \frac{1}{2}},}$ is given by

A) $R$
B) $\frac{3n\pi}{2} + \frac{3\pi}{4}$
C) $R - \left\{ \left( \frac{3n\pi}{2} + \frac{3\pi}{4} \right),n \in I \right\}$
D) None of these
Explanation

(c)
$\sin^{4}{\frac{x}{3} + \cos^{4}{\frac{x}{3} > \frac{1}{2}} \Rightarrow 1 - \frac{1}{2}\sin^{2}{\frac{2x}{3} > \frac{1}{2}}}$
$\Rightarrow \sin^{2}{\frac{2x}{3} < 1 \Rightarrow \frac{2x}{3} \in \left( R - (2n + 1)\frac{\pi}{2} \right)}$
$\Rightarrow x \in R - \left( \frac{3n\pi}{2} + \frac{3\pi}{4} \right);n \in I$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.