Math Is Fun Forum

I know that
the graph goes through the points -3,1 -1,3 and 1,4
has f'(x)= 0 at x=-1 and x=1
and f''(x)<0 for x>-1 and f''(x)>0 for x<-1

I guess it's a third degree equation?
like this? f(x)=ax³+bx²+cx+d                 

If i plug in the numbers i get
-27a+9b−3c+d=1  3=-a+b−c+d   and     4=a+b+c+d 
and
0=27a–6b+c   0=3a+2b+c   
Now i substitue, right? After substitutions i find that b = -0.3125 and a = -5/48
With these two values i can find c and d, but i think something has gone wrong..
The graph i get doesnt go through -3,1:|

help? what am I doing wrong?