Question

cos^4a+ sin^4a= 1-2cos^2sin^2

Answer 1

lhs=cos⁴a+sin⁴a=(cos²a)²+(sin²A)²
=using a²+b²=(a+b)²-2ab
=(sin²a+cos²a)-2sin²a.cos²a
we know that:sin²a+cos²a=1
=1-2sin²a.cos²a
..................................proved.................................................. please mark me brainliest