Samantha is told that sin (O) = and tan (0)<0, and was asked to determine the value of cos (©). • She uses the Pythagorean identity and defines it to be sin() + cos2 ( 0 )= 1.
• She substitutes į into the equation for sin (0)
• She then looks at values of sin ( ) and tan () and says that the only quadrant in which sin() is positive and
tan() is negative is the first quadrant.
Samantha determines that the answer is
cos () =
(21)