Найти сумму sin^4 15^0+ cos^4 15^0

Question

Найти сумму sin^4 15^0+ cos^4 15^0

Answer 1

=(sin^2 15^0+cos^2 15^0)^2-1/2*(4sin^21560*cos^2 15^0)=1-(1/2)sin^2 30^0=1-(1/2)*(1/4)=1-1/8=7/8

Answer 2

(1-cos30)²/4+(1+cos30)²/4=1/4(1-2cos30_cos²30+1+2cos30+cos²30)=
=1/4(2+2cos²30)=1/2(1+cos²30)=1/2(1+3/4)=1/2*7/4=7/8