Cos(α-90)=cos(-(90-α))=cos(90-α)=sinα
sin(α-180)=sin(-(180-α))=-sin(180-α)=-sinα
tg²(180-α)=(tg(180-α))²=(-tgα)²=tg²α
ctg²(α-180)=(ctg(-(180-α)))²=(-ctg(180-α))²=(ctgα)²=ctg²α
cos(α-90)+sin(α-180)+tg²(180-α)+ctg²(α-180)=sinα-sinα+tg²α+ctg²α=tg²α+ctg²α
tg²α+ctgα=tg²α+ctg²α
2. sin²t=(5/13)², sin²t=25/169
sin²t+cos²t=1
cos²t=1-(5/13)², cos²t=144/169
cost=+-12/13, π/2cost=-12/13
tg²t=sin²t/cos²t, tg²t=(25/169)/(144/169).
tg²t=25/144