Magnetic force on a triangular current loop

[sfgoat]

This is a question I got wrong on a test and would like to see if I can get someone to show me how to do it properly. Snapped a pic . See below please. Thanks.

 

[BruceW]

You've written $\sin(\phi )=1$ at the top. And that is true for the ac segment. But is it true for the other two segments?

 

[sfgoat]

So would the force on the bc segment be zero since the sin(pi or 2pi) would be zero

 

[BruceW]

yep, you got it. keep going :)