25(x+2)^2-30(x+2)+9=0
提出25,则25[(x+2)^2-6/5(x+2)+9/25-9/25]+9=0
25[(x+2)^2-6/5(x+2)+9/25]-25*9/25+9=0
25(x+2-3/5)^2=0
(x+2-3/5)^2=0
x+2-3/5=0
x=-7/5