Question

Доказать тождество:
ctg^2alpha - cos2alfa=ctg^2alpha*cos2alfa

Answer 1

(tga+ctg a)(1-cos ^2 2a +sin^2 2a)=4sin2a
(tga+ctga)*2sin^2 2a=4sin2a
tga+ctga=2/sin2a
sina/cosa+cosa/sina=2/sin2a
1/sinacosa=2/sin2a
2/2siacosa=2/sin2a
2/sin2a=2/sin2a