Question 852241
Given that angle X is in the first quadrant and 
cosX = 15/17
sin(X) = sqrt(17^2-15^2)/17 = 8/17
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 and angle Y terminates in the second quadrant (pi/2 < Y < pi) and 
sin Y = 12/13
cos(Y) = -sqrt(13^2-12^2)/13 = -5/13
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then find the value of cos(Y-X) in fraction form.
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cos(y-x) = cos(y)cos(x)+sin(y)sin(x) 
= (-5/13)(15/17)+(12/13)(8/17)
= (-75+96)/(13*17)
= (21)/(13*17)
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Cheers,
Stan H.
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