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Trig question confusion. 
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#1
Dec413, 03:48 PM

P: 18

Not homework just my own revision.
If sin a = –cos b = 3/5 and a and b are both in the second quadrant, what is cos (a – b)? Now keep getting the answer 0, but the answer is apparently 24/25, now they use the trig subtraction formula, I just did cos ((arcsin(3/5)  arccos(3/5)) I got 0 as the answer. Was my method wrong, where did I go wrong with it? 


#2
Dec413, 03:52 PM

Sci Advisor
P: 6,106

Both arcsin and arccos are multivalued. You need to get the possible solutions and see which are in the second quadrant.



#3
Dec413, 03:54 PM

P: 18




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