sinx/(x^2+ 1)<； = f(x)& lt； = 2+sinx/(x 2+1) [Note: the value on the left of inequality will change if a non-negative part is removed, such as (1+x 2)/(x+5) > =1(x+5), and a is used on the right.

Continue the transformation with-1/(x 2+ 1)

x^2+ 1>； = 1, 1/(x^2+ 1)<； = 1,- 1/(x^2+ 1)>； =- 1, obviously 2+sinx.

So there is-1