Cosine expression???

Question

can someone help me solve this???

1. what is the equivalent cosine expression for 5sin (wt + 50°)?

a. -5cos (wt + 50°)

b. -5cos (wt - 180°)

c. -5cos (wt - 100°)

d. -5cos (wt + 140°)

thankz! 10 pointz for the verY best answer!^_^

Answer 1

the answer is D

cosine and sine differ by 90 degree phase angle

and it is easy to check with a calculator

e.g.

cosine(45)==-sin(90+45), which is kinda what they did for answer D

Answer 2

a