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Finding horizontal tangents on an interval 
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#1
Oct2210, 01:54 PM

P: 3

1. The problem statement, all variables and given/known data
Determine all x in [pi/2, pi/2] at which the graph has horizontal tangents. 2. Relevant equations 1.) f'(x)= 9cos(x)2sin(x) 2.) f'(x)= 5csc(x) (5cot(x)csc(x)) 3. The attempt at a solution 1.) 9cos(x)=2sin(x) 9/2=sin(x)/cos(x) 9/2=tan(x) and then I'm not sure what to do with 9/2? 2.) 5cot(x)=csc(x) 5= csc(x)/cot(x) 5=1/cos(x) cos(x)=1/5 same problem here... what do I do with 1/5? 


#2
Oct2210, 03:13 PM

HW Helper
P: 925




#3
Oct2210, 03:53 PM

P: 3

I'm sorry, I still don't knowI'm not aware of a "simple" solution to tan(x)=9/2. How would I go about finding the solution?



#4
Oct2210, 04:39 PM

P: 42

Finding horizontal tangents on an interval
Look up the arctan function (also called inverse tangent) and its uses.



#5
Oct2310, 04:52 PM

P: 3

Got it. Thanks!



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