<span><span>cosa=1/√2 cos²a=1/2
sina=√1-1/2=1/√2 sin²a=1/5
cos2a=cos²a-sin²a=1/2-1/2=0
sin2a=2sinacosa=2*1/√2*1/√2=1
cos2a-coa6a=-2sin(-2a)sin4a=2sin2asin4a=2sin2a*2sin2acos2a=
=4sin²2acos2a=4*</span>1*0=0</span>
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
15+16=31
либо:
15,5+15,5 =31
2cos²2x-1+cos2x+cos6x=0
cos2(2x)+cos2x+cos6x=0
cos4x+cos2x+cos6x=0
cos4x+2*cos(6x+2x)/2*cos(6x-2x)/2=0
cos4x+2cos4x*cos2x=0
cos4x(1+2cos2x)=0
cos4x=0
4x=π*n/2
x=π*n/8
1+2cos2x=0
2cos2x=-1
cos2x=-1/2
2x=2π/3+2πn
x=π/3+πn
2x=4π/3+2πn
x=2π/3+πn