抱歉忘了檢查

(x^2) / ((x^2) - a)

= ((x^2) - a) / ((x^2) - a) + a / ((x^2) - a)

= 1 + 0.5 * (a^0.5) / (x - (a^0.5)) - 0.5 * (a^0.5) / (x + (a^0.5))