Hi
I was solving homework and the question is to draw a diagram of the in series connected inductor and resistor
I drawed my diagram different than the sample solution . I guess they are the same because the phase angle between U and I must be -90 degrees but I am not sure

 

They are equivalent, but the book's solution is generally more preferred. The positive horizontal axis is usually the reference and for a series circuit the current through the circuit is generally used as the reference waveform. However, you have all the relationships correct, and that's the important thing.