If a quadratic function has zero at x=-9, then point (-9,0) lies on the graph of quadratic function.
A line of symmetry has equation x=-3.5 that is x+3.5=0.
Use formula for the distance from point [tex](x_0,y_0)[/tex] to the line AX+By+C=0:
[tex]d=\dfrac{|Ax_0+By_0+C|}{\sqrt{A^2+B^2}}.[/tex]
Thus,
[tex]d=\dfrac{|-9+3.5|}{\sqrt{1^2+0^2}}=5.5.[/tex]
Answer: the distance is 5.5 units.
