# Thread: Determining The Principle Angle Help!?!

1. ## Determining The Principle Angle Help!?!

Hi everyone, i've gotten this question today at school and i know how to do it but i just want to know why?

The question is,

Determine the principle angel

1) -730
2) 905

When i do the first question i have to mutiply -730 by 3 to get -1080 and then i subtract it to get -350 (which is the correct answer)

When i do the seconed question i have to mutiply 360 by 2 to get 720 and subtract 905 from 720 to get 185 (which is the correct answer)

But! i dont know why one question i need to mutply by 3 and the other one i mutiply by 2. Perhaps there is a simpler method in doin this? Please help because im in desperate need! Thank you

2. You don't multiply -730 by 3.
You must always add/subtract a multiple of 360 degrees from the angle given. In this case multiply 360 by 3. Add that to your given angle to get +350 degrees for an angle between 0 and 360 degrees. Or multiply 360 by 2 and add that to your given angle to get -10 degrees for an angle between -180 and +180.

Which you want depends on how the principle angle is defined.

3. I dont really understand, mind explaining it to me once again?

Originally Posted by mnova
You don't multiply -730 by 3.
You must always add/subtract a multiple of 360 degrees from the angle given. In this case multiply 360 by 3. Add that to your given angle to get +350 degrees for an angle between 0 and 360 degrees. Or multiply 360 by 2 and add that to your given angle to get -10 degrees for an angle between -180 and +180.

Which you want depends on how the principle angle is defined.