Using De’Moivre’s Theorem, prove that
cos^4 θ= 1/8 cos4θ + 1/2 cos2θ+ 3/8
Kindly show the solution,
Thanks.
Start with:
$\displaystyle \displaystyle (\cos (\theta)+i \sin(\theta))^4= \cos(4\theta)+i\sin(4\theta)$
Expand the left hand side and equate real parts on both sides of the resulting equation. Now it should be just an exercise in the repeated application of trig identities.
CB