设表达式为:y=ax^2+bx+c 则有:
a+b+c=0 `````````````````````1
a-b+c=-4``````````````````````2
c=-3```````````````````````````3
联立1、2、3解得:a=1,b=2,c=-3
所以可得:y=x^2+2x-3
设表达式为:y=ax^2+bx+c 则有:
a+b+c=0 `````````````````````1
a-b+c=-4``````````````````````2
c=-3```````````````````````````3
联立1、2、3解得:a=1,b=2,c=-3
所以可得:y=x^2+2x-3