(x+9)^2

(x + 9)² = x² if x = -4.5

no it is 

(x+9)(x+9)=x(x+9)+9(x+9)

and you can finish it.

Thanks Alan,

Alan has interpreted the question differently from me.

He thinks that you want the solution to    $$(x+9)^2 = x^2$$

If   $${{\mathtt{a}}}^{{\mathtt{2}}} = {{\mathtt{b}}}^{{\mathtt{2}}}$$    then  $$a=\pm b$$

So either x+9=x which has no solution.

or

x+9=-x and the solution is x=-4.5