1) cos^2x=1+sin^2x 2) 4 сos^x=3

1) cos^2x = 1 + sin^2x;

cos^2x = sin^2x + cos^2x + sin^2x;

cos^2x - cos^2x = 2sin^2x;

0 = 2sin^2x;

sinx = 0;

x = pik, k ∈ Z.

Ответ: pik, k ∈ Z.

2) 4 сos^2x = 3;

cos^2x = 3/4;

cosx = + -sqrt (3/4);

cosx = + -sqrt3/2;

x = + -pi/6 + 2pik, k ∈ Z;

x = + -5pi/6 + 2pik, k ∈ Z.

Ответ: + -pi/6 + 2pik, k ∈ Z; + -5pi/6 + 2pik, k ∈ Z.