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In triangle ABC, sin A = 4/5. Find cos B.

 

 Nov 30, 2020
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Using the Law of Sines

 

sin A / 19  =sin B  / 9

 

(4/5) / 19  = sin B  / 9

 

sin B =  9(4/5) / 19

 

sin B =  36 / 95

 

cos B    = sqrt [   1 - sin^2 B ] 

 

cos  B = sqrt [  1 - (36/95)^2 ]  =  sqrt [ 95^2 - 36^2 ] / 95  = sqrt [ 7729 ] / 95

 

 

cool cool cool

 Nov 30, 2020

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