cox2x-0.75+sin^2 x= 0

cos2x-0,75+sin²x=0
cos2x-75/100+(1-cos2x)/2=0
cos2x-3/4+(1-cos2x)*1/2=0
2cos2x-3/2+1-cos2x=0
4cos2x-1-cos2x=0
3cos2x=1
cos2x=1/3
2x=±arccos1/3+2πk
x=±1/2*arccos1/3+πk;k€Z