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) ?
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) = .......