Question

tg^2a(1+tg^2a) (1+ctg^2a)-(1-tg^2a)2=4tg^2a
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Answer 1

                                   Решение:

(1+sin^2a/cos^2a)*tg^2a(1+cos^2a/sin^2a)-(1-sin^2a/cos^2a)^2=tg^2a/sin^2a*cos^2a-(1-sin^2a/cos^2a)^2=(1-(cos^2a-sin^2a)^2)/cos^4a=(1-сos^22a)/cos^4a=sin^2(2a)/cos^4a
=4sin^2acos^2a/cos^4a=4tg^2a.