Ответы и объяснения

2014-01-31T03:20:27+00:00
Sin a/(1-cos a)=(1+cos a)/sin a
Sin a/(1-cos a)-(1+cos a)/sin a=0
(Sin^2 a-(1+cos a)(1-cos a))/sin a(1-cos a) =0
(Sin^2 a-1+cos^2 a)/sin a(1-cos a) =0
(1-1)/sin a(1-cos a)= 0
0/sin a(1-cos a)=0
0=0