(1+tg^2a)*(1+cos^2a)
1+cos^2a+tg^2a+tg^2a*cos^2a=1+cos^2a+tg^2a+(sin^2a/cos^2a)*cos^2a=1+cos^2a+tg^2a+sin^2a=1+1+tg^2a=2+tg^2a