x/a-x^2-a^2/a^2*a/x+a

[tex] \frac{x}{a} - \frac{x^{2}- a^{2} }{a^{2} }* \frac{a}{x+a} = \frac{x}{a} - \frac{(x+a)(x-a)}{a^{2} }* \frac{a}{x+a}= \frac{x}{a} - \frac{x-a}{a} = \frac{x-x+a}{a} = \frac{a}{a}=1 [/tex]