There is an equation as you can see below. Here, C1, C2 and C3 denote constants, while x and y denote variables.
I want to observe the effect of x on U. In short, will increasing x increase or decrease U? How can I prove this mathematically? I tried using limit but it didn't work because of two different variables. In addition, a constraint such as 40<x<55 can be set for x.