(r^3·s^2 + 2·r^4·s^4 + r^5·s^6) / (r^3·s^3 + r^4·s^5) / ((r^2·s - r^3·s^39) / (r^2·s^2 - 2·r^3·s^4 + r^4·s^6))
= r^3·s^2·(r·s^2 + 1)^2 / (r^3·s^3·(r·s^2 + 1)) · ((r^2·s^2·(r·s^2 - 1)^2) / (r^2·s·(1 - r·s^38)))
= (r·s^2 + 1)^2 / ((r·s^2 + 1)) · (((r·s^2 - 1)^2) / ((1 - r·s^38)))
= (r·s^2 + 1)·((r·s^2 - 1)^2/(1 - r·s^38))
= (r·s^2 + 1)·(r·s^2 - 1)^2/(1 - r·s^38)