化简2cos^2(4θ)-1

化简2cos^2(4θ)-1
化简2cos^2(4θ)-1

化简2cos^2(4θ)-1

根据二倍角公式cos2a=cos²a-1得
2cos^2(4θ)-1
=cos8θ

原式=2cos^2(4θ)-(cos^2(4θ)+sin^2(4θ))
=cos^2(4θ)-sin^2(4θ)
=cos(8θ)