Cos(π/6-α)=сosπ/6*cosα+sinπ/6*sinα cosα=-15/17 sinα=-√(1-15²/17²)
15²/17²=225/289 1-225/289=64/289 √64/289=8/17 sinα= -8/17
cos(π/6-α)=-√3/2*15/17-1/2*8/17
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sinα=40/41 cosα=-√(1-1600/41²)=-9/41
sin(π/3+α)=sinπ/3*cosα+cosπ/3*sinα=-√3/2*9/41+1/2*40/41
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tg(π/4-α)=[tgπ/4-tgα]/[1+tgπ/4*tgα]=(1-tgα)/(1+tgα)
(1-tgα)/(1+tgα)=1/2 2-2tgα=1+tgα 3tgα=1 tgα=1/3