Question

Помогите пожалуйста))
2/√3 (sin^4 15°- cos^4 15°)

Answer 1

$frac{2}{ sqrt{3} }(sin^415-cos^415)= frac{2}{ sqrt{3} }((sin^215)^2-(cos^215)^2)=\\=frac{2}{ sqrt{3} }(sin^215+cos^215)(sin^215-cos^215)=\\=frac{2}{ sqrt{3} }*1*(-cos(2*15))=-frac{2}{ sqrt{3} }*cos30=-frac{2}{ sqrt{3} }*frac{ sqrt{3} }{2}=-1$