Question

What is formula of cos8x

Answer 1

Answer:

cos6x−cos8x

=2sin(

2

6x+8x

)sin(

2

8x−6x

)

=2sin7xsinx

Answer 2

Answer:

Step-by-step explanation:

Upon applying the double-angle formula for cosine three times, we have:

cos(8x) = cos[2(4x)]

= 2cos^2(4x) - 1

= 2[2cos^2(2x) - 1]^2 - 1

= 2{2[2cos^2(x) - 1]^2 - 1}^2 - 1

= 2{2[4cos^4(x) - 4cos^2(x) + 1] - 1}^2 - 1

= 2[8cos^4(x) - 8cos^2(x) + 1]^2 - 1

= 2[64cos^8(x) - 128cos^6(x) + 80cos^4(x) - 16cos^2(x) + 1] - 1

= 128cos^8(x) - 256cos^6(x) + 160cos^4(x) - 32cos^2(x) + 1.