Y = quadratic of X / quadratic of X + 1 (x belongs to R) Y value range

Y = quadratic of X / quadratic of X + 1 (x belongs to R) Y value range

It's to find the range of function
Using the separation constant method
y=x²/(x²+1)
=(x²+1 -1)/(x²+1)
=1- 1/(x²+1)
x²≥0
x²+1≥1
0