Verified answer

1)sin^2(x/4)+2sin(x/4)*cos(x/4)+cos^2(x/4)≤1/2

1+sin(x/2)≤1/2

sin(x/2)≤-1/2

-3pi/4+2pin ≤ x/2≤-pi/4+2pin;  n⊂Z

умножу все на 2

-1.5pi+4pin≤x≤-pi/2+4pin

26)sinx=t

2t^2-3t+1<0

D=9-8=1

t1=(3+1)/4=1; t2=(3-1)/4=1/2

pi/6+2pim≤x≤5pi/6+2pim; m⊂Z