Electric field above a charged square loop

[Cocoleia]

Homework Statement

Homework Equations

The Attempt at a Solution

I have the complete solutions for this problem, I just don't understand them:

This is the first part. I don't understand what r' is, or how we found it. Otherwise I understand the concept of the problem just not the details...

 

[Diegor]

Homework Statement

View attachment 113644

Homework Equations

The Attempt at a Solution

I have the complete solutions for this problem, I just don't understand them:
View attachment 113645
This is the first part. I don't understand what r' is, or how we found it. Otherwise I understand the concept of the problem just not the details...

r' is the position vector from selected origen to a charge element.

and to get the value of r' choose one point on the line and draw the vector to that point to see which are its components in x and y direction.