SOLUTION: If sin α = 4/5 and cos β = -5/13 for α in Quadrant I and β in Quadrant II, find cos(α - β)

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Question 1180320: If sin α = 4/5 and cos β = -5/13 for α in Quadrant I and β in Quadrant II, find cos(α - β)
Found 2 solutions by greenestamps, mananth:
Answer by greenestamps(13203) About Me  (Show Source):
You can put this solution on YOUR website!


sin α = 4/5 in quadrant I means cos α = 3/5.

cos β = -5/13 in quadrant II means sin β = 12/13.

Then cos(A-B)=cos(A)cos(B)-sin(A)sin(B)

Easy calculations....

Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
cos(α - β)= cos%28alpha%29cos%28beta%29+%2Bsin%28alpha%29sin%28beta%29
sin α = 4/5 in quadrant I cos α = 3/5.
cos β = -5/13 quadrant II means sin β = 12/13.
Plug the values
(3/5)(-5/13) + (4/5)((12/13)
(-3/13) + (48/85)
(-15+48)/85
33/85