Question

Prove this question
please​

Answer 1

see explanation

Explanation:

Consider the left side

`cos^(4)`A +
`sin^(4)`A - 2cos²Asin²A ← is the expansion of

= (cos²A - sin²A)²

Substitute sin²A = 1 - cos²A

= (cos²A - (1 - cos²A) )²

= (cos²A - 1 + cos²A)²

= (2cos²A - 1 )²

= right side , then proven