For normal goods, the Engel curve has a positive gradient.
2.
Still another region of positive gradient occurs at very high altitudes, in the aptly-named thermosphere above.
3.
In other words, there is a "'steeper negative gradient "'than positive gradient.
4.
In the case of an applied electrostatic field, an electron will deflect towards the positive gradient of the field.
5.
So I'm going to assume your requirement is satisfied if f ( x ) has strictly positive gradient when " x " is negative and has strictly negative gradient when " x " is positive.
मोबाइल