Magnetic field at the center of a square conducting loop

[sugz]

Homework Statement

Problem and solution attached

Homework Equations

B = [4uI/(4pi)]sin(theta1-theta2]

The Attempt at a Solution

I understand fully how to do it except determining the value of theta1 and theta2. The solution says theta1 is 45(deg) and theta2 is -45(deg). How did they get those values?

 

[TSny]

What is the geometrical interpretation of the angles θ₁ and θ₂? You might need to refer back to equation 30.4 in your textbook. There's probably a figure in the text that will be helpful.