а) 1–sin²a/cos²a–1
б) (1–cos²a)(1+tg²a)
в) sina/1+cosa + 1+cosa/sina
1-sin^2 α =cos^2 α ;
cos^2 α -1=-sin^2 α
(1-sin^2 α )/(cos^2 α -1)=cos^2 α /(-sin^2 α)= [b] - ctg^2 α [/b]
б)
1-cos^2 α =sin^2 α
1+tg^2 α =1/cos^2 α
(1-cos^2 α )*(1+tg^2 α )=sin^2 α /cos^2 α = [b]tg^2 α [/b]
в)
(sinα*sinα +(1+cosα)*(1+cosα))/((1+cosα)*sinα)=
=(sin^2α +1+2cos α +cos^2 α )/((1+cosα)*sinα)=
=(2+2cos α) /((1+cosα)*sinα)= [b]2/sin α [/b]