This circleis calledtheunit circle.Withr= 1, we can definethe trigonometricfunctionsin the unit circle:
Noticethat in the unit circle,the sine and cosineof an angleare thexandycoordinatesof the pointon the
terminalside of the angle.Now we can find the valuesof the trigonometricfunctionsof any angleof rotation,
eventhe quadrantalangles,whichare not anglesin triangles.