1)sin22,5=√(1-cos45)/2=
√(1-√2/2/2)=√(2-√2)/4=1/2*√(2-√2)
sin²75=(1-cos150)/2=(1-cos(180-30))/2=
(1+sin30)/2=(1+1/2)*1/2=3/4
OTBET 1/2*(2-√2)-3/4=1-√2/2-3/4=
1/4-√2/2
2)2cos²4x-1=0
cos8x=0
8x=π/2+πk
x=π/16+πk/8
2х² +7х + 3 = 0
D=7²-2*3*4=25=5²
х₁=(-7+5)/4=-0,5
х₂=(-7-5)/4=-3
sin2x = 2sinx*cosx ; cosx*tgx = sinx ; sin^2x*cos^2x=1