#### Answer

True

#### Work Step by Step

True
$f_{y}(a,b)=\lim\limits_{y \to b}\frac{f(a,y)-f(a,b)}{y-b}$
Suppose $h=y-b$
Then
$f_{y}(a,b)=\lim\limits_{h \to 0}\frac{f(a,b+h)-f(a,b)}{h}$
This is accordance to the definition of Limits and continuity.