Extract an expression for a couple acting on a current-carrying rectangular coil, held in a uniform magnetic field?

From the center of the loop, and the B-field is uniform,

B=2μI/4π x 2(sinα/a + sinβ/b) = μI/2π x 2(sinα/a + sinβ/b)

μ=4π*10^-7 T*m/A
I= the current
α=the angle along length a (use sinα in terms of opp/hyp if you wish)
β=the angle along length b (use sinβ in terms of opp/hyp if you wish)
a=the distance from the center to the more-wider side
b=the distance from the center to the less-wider side

There's the link to the video where this came from. Sorry that it looks completely mind-blowing. https://www.youtube.com/watch?v=wSJP0EqMLrw