[tex] \frac{2x}{x-a} [/tex]-[tex] \frac{2x}{x+a} [/tex]
[tex] \frac{2-ab}{2a+ab}[/tex]+[tex] 
x-\frac{x ^{2} }{x+1} [/tex]

[tex] \frac{7}{ x^{2} - y^{2} } - \frac{2}{xy- x^{2} } - \frac{12}{ x^{2} +xy} [/tex]
[tex] \frac{5}{(a+2 ) ^{2} } - \frac{5}{ a^{2}-4 } - \frac{5}{a+2} [/tex]