Solve left(x+3right)^2=9^2+x^2

$${ \left(x+3 \right) }^{ 2 } = { 9 }^{ 2 } + { x }^{ 2 }$$

Solve for x

$$x=12$$

Steps for Solving Linear Equation

Use binomial theorem \left(a+b\right)^{2}=a^{2}+2ab+b^{2} to expand \left(x+3\right)^{2}.

$$x^{2}+6x+9=9^{2}+x^{2}$$

Calculate 9 to the power of 2 and get 81.

$$x^{2}+6x+9=81+x^{2}$$

Subtract x^{2} from both sides.

$$x^{2}+6x+9-x^{2}=81$$

Combine x^{2} and -x^{2} to get 0.

$$6x+9=81$$

Subtract 9 from both sides.

$$6x=81-9$$

Subtract 9 from 81 to get 72.

$$6x=72$$

Divide both sides by 6.

$$x=\frac{72}{6}$$

Divide 72 by 6 to get 12.

$$x=12$$