Attiude with quaternions

Hi,

I have the following quaternions:
q1: -0.552710
q2: -0.441034
q3: -0.604951
q4:  0.366106

and the attitude with YPR
yaw: 	-97.406°
pitch: 	 20.230°
roll:  	-90.000°

but I can't figure out how to get the YPR values from the Quaternions.

Can someone explain it the easy was?

Thanks a lot
Steve

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