A) 4-3sin^2 (4x-5) = 0

b) 2sin^2 (2x) + 7cos^2 (2x) = 3

А) 4 - 3sin² (4x - 5) = 0

4 = 3sin² (4x - 5)

sin² (4x - 5) = 4/3

Нет корней, т. к. sina ∈ [-1; 1].

б) 2sin²2x + 7cos²2x = 3

2sin²2x + 2cos²2x + 5cos²2x = 3

2 + 5cos²2x = 3

5cos²2x = 1

cos²2x = 1/5

cos2x = ±√5/5

2x = ± (arccos±√5/5) + 2πn, n ∈ Z

x = ±1/2 (arccos±√5/5) + πn, n ∈ Z

(или x = 1/2 (arccos (-√5/5)) + πn и 1/2 (arccos √5/5) + πn, n ∈ Z).