f(x-1)=x^2-2x
令x'=x-1,则x=x'+1
f(x')=(x'+1)^2-2(x'+1)
f(x')=x'^2-1
∴f(x)=x^2-1
y=(x^2-2x-3)/(x+1)
y=(x+1)(x-3)/(x+1)
y=x-3,x≠-1
∴间断点是-1