Forward Kinematics Euler Angles

Does anyone have a source for how the equations for the Euler angles for forward kinematics were derived? They don't seem to match with the included picture for RotX/RotY/RotZ?

y = ATAN2((H62/I8), (G62/I8))

p = ATAN2(-I62, SQRT((I60^2)+(I61^2)))

r = ATAN2((H61/I8), (I60/I8))

Thanks!

Corey