Question

tg^2a-2tga+ctga если tga+ctga=3​

Answer 1

$tga+ctga=3\to ctga=3-tga\\tga+\frac{1}{tga}=3\\tg^2a+1=3tga\\tg^2a-3tga=1\\tg^2a-2tga=1+tga$

$tg^2a-2tga+ctga=1+tga+3-tga=4$