Question

Докажите тождество:
(tga+ctga)^2-(tga-ctga)^2=4

Answer 1

$(tga+ctga)^2-(tga-ctga)^2=4\ (tga+ctga-tga+ctga)(tga+ctga+tga-ctga)=2ctga*2tga=4*1=4\ tga*ctga=1$