Solve 9=left(9-bright)^2-b^2

$$9 = { \left(9-b \right) }^{ 2 } - { b }^{ 2 }$$

Solve for b

$$b=4$$

Steps for Solving Linear Equation

Use binomial theorem \left(a-b\right)^{2}=a^{2}-2ab+b^{2} to expand \left(9-b\right)^{2}.

$$9=81-18b+b^{2}-b^{2}$$

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

$$9=81-18b$$

Swap sides so that all variable terms are on the left hand side.

$$81-18b=9$$

Subtract 81 from both sides.

$$-18b=9-81$$

Subtract 81 from 9 to get -72.

$$-18b=-72$$

Divide both sides by -18.

$$b=\frac{-72}{-18}$$

Divide -72 by -18 to get 4.

$$b=4$$