∵a+c＝b   ①4a+c＝2b ②，∴②-①得：3a=b，c=2a，∵ax2+bx+c=0，∴x=−b±b2−4ac2a=−3a±92−4a•2a2a=−3a±a2a，∴x1=−3a+a2a=-1，x2=−3a−a2a=-2；故答案为：x1=-1；x2=-2．...