Question

cos^2*6x-sin^2*3x-1=0

Answer 1

Мое решение во вложениях) удачи) 

Answer 2

$cos^26x-sin^23x-1=0\\boxed{sin^2alpha=frac{1-cos2alpha}2}\\cos^26x-frac{1-cos6x}2-1=0\\2cos^26x-1+cos6x-2=0\\2cos^26x+cos6x-3=0\\D=1+24=25\\cos6x=frac{-1pm5}4\\cos6x=1 || cos6x=frac{-6}4 (<-1)\\6x=2pi n\\boxed{x=frac{pi n}3, nin Z}$