A1. The domain of the function $f(x)=\frac{x}{x^{2}+(a+1) x+b}$ is $\mathbb{R} \backslash\{-2\}$. What is the value of the expression $5 a-3 b$?
(A) 3
(B) 7
(C) 11
(D) 13
(E) 27
A1. From the condition of the problem, it follows that $x^{2}+(a+1) x+b=(x+2)^{2}=x^{2}+4 x+4$. Therefore, $a+1=4$ or $a=3$ and $b=4$. It follows that $5 a-3 b=5 \cdot 3-3 \cdot 4=3$.