$${ \left(x+4 \right) }^{ 2 } - { \left(x-5 \right) }^{ 2 } =9$$
$x=1$
$$x^{2}+8x+16-\left(x-5\right)^{2}=9$$
$$x^{2}+8x+16-\left(x^{2}-10x+25\right)=9$$
$$x^{2}+8x+16-x^{2}+10x-25=9$$
$$8x+16+10x-25=9$$
$$18x+16-25=9$$
$$18x-9=9$$
$$18x=9+9$$
$$18x=18$$
$$x=\frac{18}{18}$$
$$x=1$$
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