Question

Solve the following equations.
$\tan x\tan 3x=1.$

Answer 1

$\cos x\cos 3x-\sin x\sin 3x=0$

$\cos 2x=0$

$⟹2x=(2n+1)\frac{\pi }{2},$

$⟹x=(2n+1)\frac{\pi }{4}.$