SOLUTION: I cannot for the life of me figure these out, please help! given sin a = 4/5 in quadrant I and cos ß = 12/13 in quadrant II find cos a+ß given cos a = -24/25 in quadrant II a

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Question 864456: I cannot for the life of me figure these out, please help!
given sin a = 4/5 in quadrant I and cos ß = 12/13 in quadrant II find cos a+ß
given cos a = -24/25 in quadrant II and sin ß = -5/13 in quadrant III, find sin (a+ß)
Answer by ewatrrr(24785)   (Show Source): You can put this solution on YOUR website!


Hi

given sin a = 4/5 in quadrant I and cos ß = ???12/13 in quadrant II find cos a+ß 



given cos a = -24/25 in quadrant II ⇒ sin a = 7/25    

and sin ß = -5/13 in quadrant III   ⇒ cos ß = -12/13

cos(a + ß) = cos a cos ß  -  sin a sin ß     (substitute appropriate values)

           = (-24/25)(-12/13) - (7/25)(-5/13)   

           = (24*12+35)/25*13 

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