When a quadratic equation is in the form f(x) = a(x - h)2 + k , the vertex is (h, k)
For this problem, they tell us the vertex is (-1, 5) , so we know that
f(x) = a(x - -1)2 + 5
f(x) = a(x + 1)2 + 5
We know it goes through the point (2, -13) , which means f(2) = -13
f(2) = a(2 + 1)2 + 5 And f(2) = -13
-13 = a(2 + 1)2 + 5
-13 = 9a + 5
-18 = 9a
-2 = a
Now we've found a , so we know that
f(x) = -2(x + 1)2 + 5 And here's a graph to check it.