Question

3 cos² x-  sin² x-1= 0

Answer 1

$3cos ^{2} x-sin ^{2}x-1=0\ 3cos ^{2} x-(1-cos ^{2}x)-1=0\ 3cos ^{2} x-1+cos ^{2}x-1=0\ 4cos ^{2}x-2=0\ cos ^{2} x= frac{1}{2}\ x=+-arccos sqrt{ frac{1}{2} } + pi k\ x=+- frac{ pi }{4} + pi k$