$\frac{-\frac{y-g}{x-k}-g+y}{\left(x^2-k^2\right)-\frac{x^2-k^2}{x-k}}$
Simplyfing fraction I arrived at this form:
$\frac{-\frac{y-g}{x-k}-g +y}{(x-k) (x+k)-(x+k)}$
I know it can be further simplified to
$\frac{g-y}{k^2-x^2}$
But I don't see how. I can't see how you can get rid of the substraction in denominator. Is it even possible? Maybe the result is wrong?
$$ \eqalign{ & {{ - {{y - g} \over {x - k}} - g + y} \over {\left( {x^{\,2} - k^{\,2} } \right) - {{\left( {x^{\,2} - k^{\,2} } \right)} \over {x - k}}}} = \cr & = {{\left( {y - g} \right)\left( {1 - {1 \over {x - k}}} \right)} \over {\left( {x^{\,2} - k^{\,2} } \right)\left( {1 - {1 \over {x - k}}} \right)}} = \cr & = {{y - g} \over {x^{\,2} - k^{\,2} }} \cr} $$