y=ax^2+bx+c(a/=0)
-1=c
1=a+b+c
4=4a+2b+c
a+b=2
4a+2b-1=4
4a+2b=5(1)
2a+2b=4(2)
(1)-(2) 2a=1
a=1/2
b=3/2
c=-1
y=1/2x^2+3/2x-1