# If $0\leq x\leq \large\frac{\pi}{2}$ and $81^{\large \sin^2x}+81^{\large\cos^2x}=30$ then $x$ is equal to
$(a)\;\large\frac{\pi}{6}$$\qquad(b)\;\large\frac{\pi}{2}\qquad(c)\;\large\frac{\pi}{4}\qquad$$(d)\;0$