1)1+ctg²α=1/sin²α
2) cos²α * (1/cos²α)=1
3) 1 - (1/sin²α) = 1 -(1+ctg²α)=-ctg²α
4) 4-1=3
5) cos²x(1-sin²x)=cos²x * cos²x = cos⁴x
6) sin²x(sin²x+cos²x)=sin²x
7) (tgα*ctgα)² - sin²α = 1 - sin²α = cos²α
8) sin²x / (-cos²x) = -tg²x
9) (cosα*sinα+cosα)/(sinα(1+sinα))=
= [cosα(sinα+1)] / [sinα(1+sinα)]=ctgα
10) sin²α * (1/cos²α)=tg²α