Answer:
False
Explanation:
A function is said to be differentiable over a given region if the function is continuous and has only one value for each input.
Therefore in order to conclude that f is differentiable at (a, b), the partial derivatives must be continuous at (a, b).
It is true that the function has to be defined over a given region because without it, you cannot determine if a partial derivative is continuous or otherwise.
But the fact that the partial derivatives exist at a point is not a sufficient condition for continuity.