[tonklaZolo]

$1.\frac{2cos2x}{2sin^2x-sin2x-2} =1$ จงหา $1+cos2x$
$2\cos2x=(2\sin^22x-1)-sin2x-1$
$sin2x=-3cos2x-1$
.......แทน $sin2x=\sqrt{1-cos^22x}$
แก้ได้ $cos2x=\frac{-3}{5}$
$\therefore 1+cos2x=\frac{2}{5}$