Question 852857
 find the exact value of the trigonometric function, 
cos(u+v) = cos(u)cos(v)-sin(u)sin(v) 
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sin(u) = 5/13 
cos[sqrt(13^2-5^2)]/13 = 12/13
Note: This implies that u is in QI

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cos(v) = -3/5
sin(v) = sqrt(25-9)/5 = 4/5
Note: This implies that v is in QII
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cos(u+v) = cos(u)cos(v)-sin(u)sin(v) 
= (12/13)(-3/5) - (5/13)(4/5)
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= (-36 - 20)/65
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= -56/65
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= -0.8615
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Cheers,
Stan H.
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