1) The directional derivative \( D_{u} f(x, y) \) is:
A. A number
B. A vector
C. Both A and B are correct
2) The gradient \( \nabla f(x, y) \) is:
A. A number
8. A vector
C. Both A and B are correct
3) The partial derivative \( f_{x}\left(x_{0}, y_{0}\right) \) can be understood as:
A. the rate of change
B. The slope of the tangent line
C. Both A and B are correct
4) How many second order partial derivatives does \( f(x, y, z) \) have?
A. 6
B. 7
C. 8
D. 9
5) Another notation of \( f_{x y}(x, y) \) is:
A. \( \frac{\hat{\partial}^{2} f}{\partial x \hat{\partial} y} \)
B. \( \frac{\partial^{2} f}{\partial y \partial x} \)
C. \( \frac{\partial f^{2}}{\partial y \partial x} \)
D. \( f_{y x}(x, y) \)
