2 9*b a - a*b -----*-------- a - b 45*b
2 a - a*b --------- 5*(a - b)
2 a a*b -- - --- 5 5 -------- a - b
0.2*(a^2 - a*b)/(a - b)
2 a - a*b ---------- -5*b + 5*a
a - 5