Another question, I'm really sorry.
2.) Let z=cis(a)
a.) Use De Moivre's theorem to show that z^n + (1/z)^n = 2cos(na)
I was able to prove this part.
b.) Use the binomial theorem to expand (z + (1/z))^4
I got z^4 + 4z^2 +6 +(4/z^2) + (1/z^4), is it right?
Part 2, Hence show that cos^4(a) = (1/8) (cos(4a) + 4cos(2a) + 3 and find the integral of cos^4(a)da.
I'm not sure how to show..
Thank you so so much!