SOLUTION: Given that Sin A = 4/5, 0 < A < π/2 and Cos B = -12/13, π< B < 3π/2, find Cos (A - B)
a.) -56/65 b.) 56/65
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Question 824857: Given that Sin A = 4/5, 0 < A < π/2 and Cos B = -12/13, π< B < 3π/2, find Cos (A - B)
a.) -56/65 b.) 56/65 c.) 63/65 d.) -63/65
Answer by lwsshak3(11628) (Show Source): You can put this solution on YOUR website!
Given that Sin A = 4/5, 0 < A < π/2 and Cos B = -12/13, π< B < 3π/2, find Cos (A - B)
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Identity: cos(A-B)=cosAcosB+sinAsinB
sinA=4/5 (working with (3-4-5) reference right triangle in quadrant I in which sin and cos>0.
cosA=3/5
..
cosB=-12/13 (working with (5-12-13) reference right triangle in quadrant III in which sin and cos<0.
sinB=-5/13
..
ans: a) -56/65
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