5x^2-9x=18
x^2-9x/5=18/5
x^2-9x/5 +（9/10)^2 =18/5+(9/10)^2
(x-9/10)^2=9/2
x-9/10=±3√2/2
x=±3√2/2+9/10
x=3√2/2+9/10
x=-3√2/2+9/10