移项得
6.25x^2-150x+900=0
(2.5x)^2-2*2.5*30+(30)^2=0
(2.5x-30)^2=0
2.5x-30=0
x=12 移项得
6.25x^2-150x+900=0
(2.5x)^2-2*2.5*30+(30)^2=0
(2.5x-30)^2=0
2.5x-30=0
x=12