Ответы и объяснения

2013-10-30T06:21:51+00:00
2) =(1-cosy /siny)^2-1/sin^2 y=((siny-cosy)^2/sin^2y-1/sin^2 y=(sin^2y-2sin y cos y+cos^2y-1) /sin^2 y=-2siny cosy /sin^2y=-2cosy/siny=-2ctgy
3)=(1*cos^2t)/((1-cost)(1+cost))=cos^2 t /(1-cos^2 t)=cos^2 t /sin^2 t=ctg^2 t