Question

Cos4 A = 8 cos⁴A - 8 Cos²A+I​

Answer 1

Answer:

LHS= Cos4A=Cos2(2A)

2Cos^2A-1

2(2Cos^2A-1)^2-1

2(4Cos^4A+1-4Cos^2A)-1

8cos^4A+2-8Cos^2A-1

8Cos^4A-8Cos^2A-1=RHS

Hence proved