Question

If 2 cos 3$\theta$ = 1 then $\theta$ = ?

(a) ${10}^o$ (b) ${15}^o$ (c) ${20}^o$ (d) ${30}^o$

Answer 1

$2cos3\theta =1$

$cos3\theta =\frac{1}{2}$

$cos3\theta =cos{60}^o$

$3\theta ={60}^o$

$\theta =\frac{60}{3}={20}^o$

$\theta ={20}^o$