ax^2+bx+c=0ax^2+bx=-cx^2+bx/a=-c/ax^2+2*x*(b/2a)+(b/2a)^2=-c/a+(b/2a)^2(x+b/2a)^2=(b^2-4ac)/4a^2x+b/2a=±√(b^2-4ac)/2ax=[-b±√(b^2-4ac)]/2a令判别式△=b^2-4ac 当△0时,有两个根