12X*9(10-X)=1
1080x-108x^2=1
108x^2-1080x+1=0
x = {1080±根号(1080^2-4*108) } / (2*108) = { 90±根号(90^2-3) } / 3 = 30 ± (根号8097)/3
x1 = 30 - (根号8097)/3
x2 = 30 + (根号8097)/3