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