Which of the following is a positive angle that is coterminal with 13 pi over 9

Question

Choices are ;

 

-31 pi over 9

 

-5 pie over 9

 

5 pie over 9

 

31 pi over 9

Answer 1

The coterminal angle of a positive angle is the complement to 360 degrees or 2∏ plus the angle in this case the angle base is 13∏/9 and if we add 5∏/9 we obtain 18∏/9 which is 2∏. then the answer is  ((5∏/9)+13∏/9))= 2∏

Answer 2

Coterminal is just a fancy trig term for "in the exact same spot" as the given angle. We know that adding/subtracting 2pi will make a complete revolution and leave us in the same spot that we started. But it changes our angle by a factor of 2pi.

 

They ask for a positive angle, so we should add 2pi to 13pi/9:

 

18pi/9 + 13pi/9 = 31pi/9