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Angle α lies in quadrant II , and tanα= −12/5. Angle β lies in quadrant IV , and cosβ= 3/5. What is the exact value of cos(α−β) ?

 

cos(α-β)

 Mar 10, 2020
 #1
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In Q II    sin is positive    cosine is negative

  if tan =-12/5     sin = pos     cos =negative            sin a= 12/13  cos a = -5/13 

 

For Q IV   sin b is negative cos b is positive    and   cos^2 + sin^2 = 1    yields sin b = -4/5

 

  

        cos (a-b) = cos a cos b  + sina sinb

                        -5/13 ( 3/5)  +  12/13 (-4/5) = .......

 Mar 10, 2020

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