ax²+bx+c=0x²+b/ax+c/a=0x²+2*(b/2a) x=-c/ax²+2*(b/2a) x+(b/2a)²=(b/2a)²- c/a(x+b/2a)²=(b²-4ac)/4a²x+b/2a=正负根号下(b²-4ac)/4a²=2a分之根号下(b&sup...