i have to solve this problem and then put restrictions on it

**4a^2-b^2-2a+b / (2a+b)^2-1**

the answer is 2a+b / 2a+b+1

but on my answer sheet the restrictions also says

**b is not equal to 1-2a and -(2a+1)**

my teacher also said it is

**2a+b not equal to -1**

i dont know how to find restrictions -____-