<PRE><B>Question 855933</B>
How would I find cos(x-y) if cos x= 3/5 and cos y= 4/5 when the exact value needs to be between 0 and 90 degrees.
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If cos(x) = 3/5, sin(x) = sqrt(5^2-3^2)/5 = 4/5
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If cos(y) = 4/5, sin(y)= sqrt(5^2-4^2)/5 = 3/5
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cos(x-y) = cos(x)cos(y)+ sin(x)sin(y) = (3/5)(4/5)+(4/5)(3/5)
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= (12+12)/25 = 24/25
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Cheers,
Stan H.</PRE>