A) 4cos^2 x = 3-4cosx

b) 2sin^2 x + 3cosx - 3 = 0

А

4 сos²x+4cosx-3=0

cosx=a

4a²+4a-3=0

D=16+48=64

a1 = (-4-8) / 8=-1,5⇒cosx=-1,5<-1 нет решения

a2 = (-4+8) / 8=1/2⇒cosx=1/2⇒x=+-π/3+2πn, n∈z

b

2-2cos²x+3cosx-3=0

cosx=a

2a²-3a+1=0

D=9-8=1

a1 = (3-1) / 4=1/2⇒cosx=1/2⇒x=+-π/3+2πn, n∈z

a2 = (3+1) / 4=1⇒cosx=1⇒x=2πk, k∈z