Question

( tg a+ctg )^{2} - ( tg a - ctg )^{2}  

Answer 1

( tg a+ctg )^{2} - ( tg a - ctg )^{2}=(tg a+1/tg)^2-(tg a - 1/tg a)^2=((tga^2+1)^2-(tga^2-1)^2)/tga^2=4