Bug, error, or junk

[Davidy]

Well, I mentioned x and y to indicate the vertical and horizontal legs of the triangle.

Anyway, dumb me (I have just started using the Prime and haven't read the manual) but with further experimentation, I have found that the formulae won't accept a zero in the unknown boxes, you have to actually erase (backspace) any unknowns and only make entries in the known spaces.

All my other HPs were fairly intuitive, this one isn't. Maybe I should read the manual.