Step-by-step explanation:
[tex]cos ^{2} x - \sin ^{2} x = \frac{1}{3} [/tex]
[tex] \frac{(cos ^{2}x - \sin ^{2} x)(cos ^{2}x + \sin ^{2} x)}{(cos ^{2}x + \sin ^{2} x)} = \frac{1}{3} [/tex]
[tex] \frac{(cos ^{4}x - \sin ^{4} x)}{1} = \frac{1}{3} [/tex]
as cos²x+sin²x=1
Hence
cos⁴x-sin⁴x=1/3
