If f(x)=(x-B)/(x=A) and f(2)=0 and f(1) is undefined what is A and B?
You meant $\displaystyle f(x)=\frac{x-B}{x-A}$, right? I'm assuming the
"=" was a mistake.
We know that: $\displaystyle f(2)=\frac{2-B}{2-A}=0$ and that $\displaystyle f(1)=\frac{1-B}{1-A}$ is undefined. If f(1) is undefined, that means that we will be dividing by zero, such that $\displaystyle A=1$.
We can now substitute A for 1:
$\displaystyle f(2)=\frac{2-B}{2-1}= 0$
$\displaystyle 2-B=0$
$\displaystyle B=2$