1.(1-sint)(1+sint)=?
2.(cosx+1/2)(cosx-1)=0

1)  (1 - sint)*(1 + sint) = 0
a) 1 - sint = 0
 sint = 1
t = π/4 + πk, k∈Z
b) 1 + sint = 0
 sint = - 1
t = - π/4 + πn, n∈Z 
 2)  (cosx + 1/2)(cosx - 1 )= 0
a) cosx + 1/2 = 0
 cosx = - 1/2
x = (+ -)arccos(-1/2) + 2πn, n∉Z
x = (+ -)*(π - arccos(1/2)) + 2πn, n∉Z
x = (+ -)*(π - π/3) + 2πn, n∉Z
x = (+ -)*(2π/3) + 2πn, n∉Z
b)  cosx - 1 = 0
cosx = 1
x = 2πk, k∈Z