The total differential
Task number: 3199
Determine whether the given functions have a total differential at the point \((x, y) = (0, 0)\) and write down the associated coefficients.
Variant 1
\((1 + x)^k (1 + y)^{\ell}\), where \(k, \ell \in \mathbb N\) are parameters.
Variant 2
\(\ln (1 + x) \ln (1 + y)\)
Variant 3
\((1 + x)^{1 + y}\)
