Question

determine whether the equation is an identity

cos^4θ+1-sin^4θ=2cos^3θ

Answer 1

\[is the equation is \cos4\theta+1-\sin4\theta=2\cos3\]

Answer 2

\[\cos ^4 \theta+1-\sin ^4\theta=2 \cos ^3\theta\]

Answer 3

\[x^4-y^4=(x^2-y^2)(x^2+y^2)\]
\[\cos ^4\theta-\sin ^4\theta=(\cos ^2\theta-\sin ^2\theta)(\cos ^2\theta+\sin ^2\theta)=(\cos ^2\theta-\sin ^2\theta)(1)\]
\[\cos ^2\theta-\sin ^2\theta+1=\cos ^2\theta+1-\sin ^2\theta=\cos ^2\theta+\cos^2\theta=2\cos^2 \theta\]

Answer 4

so no