SOLUTION: use the cosine of a sum and cosine of a difference identities to find cos (s+t) and cos (s-t). sin s = -5/13 and sin t=4/5, s in quadrant 3 and quadrant 1

Algebra ->  Trigonometry-basics -> SOLUTION: use the cosine of a sum and cosine of a difference identities to find cos (s+t) and cos (s-t). sin s = -5/13 and sin t=4/5, s in quadrant 3 and quadrant 1       Log On


   

Question 1154950: use the cosine of a sum and cosine of a difference identities to find cos (s+t) and cos (s-t). sin s = -5/13 and sin t=4/5, s in quadrant 3 and quadrant 1
Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


5-12-13 is a Pythagorean Triple; sin s = -5/13 in quadrant III means cos s is -12/13.

3-4-5 is a Pythagorean Triple; sin t = 4/5 in quadrant I means cos t = 3/5.

Use the values you now have to find cos (s+t) and cos(s-t):
cos%28s%2Bt%29+=+cos%28s%29%2Acos%28t%29-sin%28s%29%2Asin%28t%29
cos%28s-t%29+=+cos%28s%29%2Acos%28t%29%2Bsin%28s%29%2Asin%28t%29