Cosa=2/5
sina=√(1-cos²a)=√(1-4/25)=√(21/25)=√21/5
sin2a=2sinacosa=2*2/5*√21/5=4√21/25
cos2a=cos²a-sin²a=4/25-21/25=-17/25
tga=sina/cosa=√21/5:2/5=√21/5*5/2=√21/2
cos(π/3+a)=cosπ/3cosa-sinπ/3sina=1/2*2/5-√3/2*√21/5=1/5-3√7/10=(2-3√7)/10
sin(a-π/6)=sinacosπ/6-cosasinπ/6=√21/5*√3/2-2/5*1/2=3√7/10-1/5=(3√7-2)/10
Х=2+2+1
У=5-2-1
Х=5
У =2
2×5× (5×2+2)+(5×2+2)+(5×2-1)=141
0.6+(0.5у - 1) = у+0.5
0.6+0.5у-1=у+0.5
0.5у-у= 0.5+1-0.6
-0.5у=1.9
у= 1.9: (-0.5)
у= -3.8