[tex]\displaystyle{ \frac{x-1}{x+1}+ \frac{3x + 2}{ x+1}=\frac{x-1+3x+2}{x+1} }[/tex]
[tex]\displaystyle{ =\frac{4x+1}{x+1} }[/tex]
[tex]\it \dfrac{x-1}{x+1}+\dfrac{3x+2}{x+1}=\dfrac{x-1+3x+2}{x+1}=\dfrac{4x+1}{x+1}[/tex]
