Упростите выражение: (sin^2t-1)/(cos^2t-1) + tgt•ctgt.

(sin^2t-1)/(cos^2t-1) + tgt•ctgt=

=(sin^2t-sin^2t-cos^2t)/(cos^2t-sin^2t-cos^2t)+1=

=(-cos^2t/-sin^2t)  +1=(cos^2t/sin^2t)+1=(cos^2t+sin^2t)/sin^2t=1/sin^2t