Solve for x
x=5
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x^{2}=81-18x+x^{2}+9
Use binomial theorem \left(a-b\right)^{2}=a^{2}-2ab+b^{2} to expand \left(9-x\right)^{2}.
x^{2}=90-18x+x^{2}
Add 81 and 9 to get 90.
x^{2}+18x=90+x^{2}
Add 18x to both sides.
x^{2}+18x-x^{2}=90
Subtract x^{2} from both sides.
18x=90
Combine x^{2} and -x^{2} to get 0.
x=\frac{90}{18}
Divide both sides by 18.
x=5
Divide 90 by 18 to get 5.
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