Question

If $A=\{x:\frac{\pi }{6}\le x\le \frac{\pi }{3}\}$ and $f\left(x\right)=cosx$ then$f\left(\frac{\pi }{4}\right)$ is equal to-

• A. $\frac{1}{2}$
• B. $\frac{1}{\sqrt{2}}$
• C. $\frac{1}{3}$
• D. $\frac{1}{5}$

Answer 1

The correct option is B $\frac{1}{\sqrt{2}}$

Given $f\left(x\right)=\cos x$

$⟹f\left(\frac{\pi }{4}\right)=\cos \frac{\pi }{4}$

$⟹f\left(\frac{\pi }{4}\right)=\frac{1}{\sqrt{2}}$