Решите, пожалуйста
Картинка прилагается

sin a - cos a = 1/2
(sin a - cos a)^2 = sin^2 a - 2sin a*cos a + cos^2 a = (1/2)^2 = 1/4
2sin a*cos a = sin 2a = 1 - 1/4 = 3/4
1^2 = (sin^2 a + cos^2 a)^2 = sin^4 a + cos^4 a + 2sin^2 a*cos^2 a
1 = sin^4 a + cos^4 a + (2sin a*cos a)^2/2 = sin^4 a + cos^4 a + 1/2*sin^2(2a)
sin^4 a + cos^4 a = 1 - 1/2*sin^2(2a) = 1 - 1/2*9/16 = 1 - 9/32 = 23/32