Sign of a second partial derivative

[LCSphysicist]

Homework Statement

All below

Relevant Equations

All below.

I am not sure how to determine the sign of this derivatives.
(a) first we can pass a plane by (1,2) parallel to XZ (y fixed) and see how the curve belongs to the plane will vary with x, but what about the next partial derivative, with respect to y?

 

[FactChecker]

At the point, look at the slope with respect to x. When the point moves slightly in the positive y direction, does the slope with respect to x increase or decrease?