ребята помогите (1-sin^4(a)-cos^4(a))*(1+tg^2(a))=2sin^2(a)

1+tg^2(a)=1/cos(a)^2

2sin^2(a)=1-cos(2*a)

(1-sin^4(a)-cos^4(a))=2*cos(a)^2-2*cos(a)^4

(2*cos(a)^2-2*cos(a)^4)*(1/cos(a)^2)=1-cos(2*a)

(2*cos(a)^2-2*cos(a)^4)*(1/cos(a)^2)-1-cos(2*a)=0

(1+sin^2(a)-cos^2(a)=(1-cos^2(a)+sin^2(a)

sin^2(a)+sin^2(a)=2sin^2(a)

4td