5x^2+30x+45-根号5x-3根号5＝0
5(x+3)^2-根号5（x+3)==0
(x+3)[5(x+3)-根号5〕＝0
（x+3)(5x+15-根号5）＝0
x1=-3,x2=－3＋(根号5)/5