#### Answer

$$3x^{2}+2xb−b^{2}$$

#### Work Step by Step

Initially: $4x^{2}−(x-b)^{2}$ First, rewrite the $(x-b)^{2}$ in its expanded form: $(x-b)(x-b)$ Then FOIL it:
$$4x^{2}−(x^{2}-2xb+b^{2})$$
After that, distribute the negative:
$$4x^{2}−x^{2}+2xb−b^{2}$$
Then simplify by combining like terms:
$$3x^{2}+2xb−b^{2}$$