Answer :

Answer:

Step-by-step explanation:

In Q III   sin AND cos are negative

Trig identity:

    sin^2 + cos^2 =  1

       (-4/5)^2  + cos^2 = 1

                           cos^2 = 1 - 16/25

                               cos^2 = 9/25

                               cos = +- 3/5

                      BUT remember, cos is NEGATIVE in Q III

                            so the answer is   - 3/5

(I would note that  5 radians is in Q IV not Q III.....is that supposed to be a different measure of radians???)