above or:
Set up a table so that we got t(1)=2, x=2at where a=0.25 =1/2(t)=1 then y= 1^2=1
For t(2)=-1/2, x=2at so =1/2(t)=-1/4 then y= 1/16
So now you got (x2,y2) and (x1,y1)
Now just use (y-y1)/(x-x1)=(y2-y1)/(x2-x1) [2 point form]
EDIT: LOL, didn't look properly at the above...