(x²+10x+25)/(x²+4x-5)
x²+4x-5≠0
x²+5x-x-5≠0
x(x+5)-(x+5)≠0
(x+5)(x-1)≠0
x+5≠0 ∨ x-1≠0
x≠-5 ∨ x≠1
D=R\{-5,1}
(x²+10x+25)/(x²+4x-5)=(x²+2x·5+25)/(x²+5x-x-5)=(x²+2x·5+5²)/(x(x+5)-(x-1))=
=(x+5)²/((x+5)(x-1))=(x+5)/(x-1)
(x+5)/(x-1)=(-2+5)/(-2-1)=3/-3=-1
