问题标题：
若已知抛物线上三点坐标为(1,0);(-1,-4);(0,-3)求其表达式
问题描述：
若已知抛物线上三点坐标为(1,0);(-1,-4);(0,-3)求其表达式
苏竞秀回答：
设表达式为：y=ax^2+bx+c则有：a+b+c=0`````````````````````1a-b+c=-4``````````````````````2c=-3```````````````````````````3联立1、2、3解得：a=1,b=2,c=-3所以可得：y=x^2+2x-3
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