If you graph the three given points, you can see that the vertex (h,k) is (-1,3).
Equation of a quadratic function is: y = a(x - h)² + k
Plug in the vertex and one of the points (I chose (0,1)) and solve for "a".
1 = a(0 + 1)² + 3
-2 = a
Answer: f(x) = -2(x +1)² + 3
