Express with rational denominator`(a+xsqrt(-1))/(a-xsqrt(-1))-(a-xsqrt(-1))/(a+xsqrt(-1))`

Explanation

`(a=xsqrt(-1))/(a-xsqrt(-1))-(a-xsqrt(-1))/(a+xsqrt(-1))`
`=(x+ix)/(a-ix)-(a-ix)/(a+ix)=((a+ix)^2-(a-ix)^2)/((a-ix)(a+ix))`
`=(4aix)/(a^2-i^2x^2)=(4aix)/(a^2+x^2)`