[tex]=\frac{(a-b)(a-b-2c)}{(a-b+2c)(a-b-2c)}-\frac{(a-b)(a-b+2c)}{(a-b-2c)(a-b+2c)}[/tex]
[tex]a-b=t [/tex]
[tex]=\frac{t(t-2c)}{(t+2c)(t-2c)}-\frac{t(t+2c)}{(t-2c)(t+2c)}[/tex]
[tex]=\frac{t(t-2c)-t(t+2c)}{(t-2c)(t+2c)}[/tex]
[tex]=\frac{{t}^{2}-2tc-{t}^{2}-2tc}{{t}^{2}-4{c}^{2}}[/tex]
[tex]=\frac{-4tc}{{t}^{2}-4{c}^{2}}[/tex]
[tex]=-\frac{4c(a-b)}{{(a-b)}^{2}-4 { c}^{2}}[/tex]
