`P = (1+\sqrt{a})/(1-\sqrt{a}) - (1-\sqrt{a})/(1+\sqrt{a})` `(a\geq0;a\ne1)`
`P=((1+\sqrt{a})^2 - (1-\sqrt{a})^2)/((-\sqrt{a}+1)(\sqrt{a}+1))`
`=frac{[1+\sqrt{a}-(1-\sqrt{a})].[1+\sqrt{a}+(1+\sqrt{a})]}{(1-\sqrt{a})(1+\sqrt{a})}` `=frac{(1+\sqrt{a}-1+\sqrt{a}).(1+\sqrt{a}+1+\sqrt{a})}{(1-\sqrt{a})(1+\sqrt{a})}`
`=frac{2\sqrt{a}.(2+2\sqrt{a})}{(1-\sqrt{a})(1+\sqrt{a})}`
`=frac{4\sqrt{a}+4a}{(1-\sqrt{a})(1+\sqrt{a})}`
`=frac{4\sqrt{a}.(\sqrt{a}+1)}{(1-\sqrt{a})(1+\sqrt{a})}`
`=frac{4\sqrt{a}}{1-\sqrt{a}}`
