Question

Solve :-
$x^2-2\cos \alpha +\cos 2\alpha =0$.

Answer 1

Now,

$x^2-2\cos \alpha +\cos 2\alpha =0$

or, $x^2-2\cos \alpha +{\cos }^2\alpha -{\sin }^2\alpha =0$

or, $(x-\cos \alpha {)}^2={\sin }^2\alpha$

or, $x=\cos \alpha \pm \sin \alpha$.