Question

What is the axis of symmetry of the function of -(x+9)(x-21)

Answer 1

expand
-x^2+12x+189

now
the axis of symmetry is -b/2a for ax^2+bx+c

so

-1x^2+12x+189
a=-1
b=12

-b/2a=-12/(2*-1)=-12/-2=6
the axis of summetry is x=6