Answer:
-6
Step-by-step explanation:
A parabola is vertex form is written as
y = a(x-h)^2 +k where (h,k) is the vertex
Substituting in the vertex
y = a(x-5)^2 +5
We know a point on the parabola so we can find a
-1 = a( 6-5)^2 +5
-1 =a(1)^2+5
-1 = a +5
Subtract 5 from each side
-1-5 = a
-6 =a
