Question

ctg^2(a+pi/2)*cos^2(a-pi/2)/ctg^2(a-pi/2)-cos^2(a+pi/2)

Answer 1

ctg^2(a+pi/2)*cos^2(a-pi/2)/ctg^2(a-pi/2)-cos^2(a+pi/2)=tg^2a*sin^2a/tg^2a -sin^2a=sin^2a-sin^2a=0