You can either solve the pythagorean theorum repeatedly or you can get straight to the point with trig functions. It makes little sense in my brain when represented with 5 different pythagorean equations, and a lot more sense when the trig relations are used.
You get the same result either way, so there are several right answers here.
I made this little drawing in illustrator to show what makes sense in my smooth brain. (the y_skew formula below is the only one Bambu is using at the moment, in a slightly convoluted way)
