Question

The axis of symmetry for the graph of the function is f(x) = x2 + bx + 10 is x = 6. What is the value of b?

Answer 1

-12
The axis of symmetry is a vertical line x=(-b)/(2a)
You know the following:
x=6
a=1 (because x squared has no coefficient, therefore is automatically 1)
b=unknown
Now you input.

6=(-b)/(2*1)
multiply bottom
6=(-b)/2
multiply by reciprocal of denominator
2*6=(-b/2)*(2/1)
cross out and multiply
12=-b
multiply both sides by -1 to cancel out the -b
-12=b
so
b =-12