m 18 -------- - -------- 2 2 (k - 9) (9 - k)
-18.0/(9.0 - k)^2 + m/(-9.0 + k)^2
2 2 - 18*(-9 + k) + m*(9 - k) --------------------------- 2 2 (-9 + k) *(9 - k)
-18 + m --------- 2 (-9 + k)
-18 + m -------------- 2 81 + k - 18*k