Need some help identifying the increase intervals of the graph of xtanx

- anonymous

Need some help identifying the increase intervals of the graph of xtanx

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- anonymous

|dw:1349987981581:dw|

- Venomblast

is this in radian?

- anonymous

i know this is a even function about the y axis, and the domain and asymptotes are pi/2,-pi/2

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- anonymous

just wondering how to show the intervals of increase and decrease

- Venomblast

so -90 degrees

- anonymous

usually i take f'x and solve for 0

- Venomblast

i see

- Venomblast

i see no 0. is this is an equation?

- anonymous

f'x=tanx+xsec^2x

- anonymous

@zepdrix hey do you think you could explain how they designate zero as a critical point?

- anonymous

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- anonymous

should i just know that, from the x and y intercepts and the even symetry? and a basic knowledge of the tanx graph?

- anonymous

because when i set my derivative = 0 i have problems

- zepdrix

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Hmm yah this derivative does seem to be putting up a fight :\
Hmmmmm

- anonymous

i tried changing everything to sines and cosines and still a mess

- zepdrix

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Ah good call, I think that's how you find it! :)
The top is a big mess, yes.
But the bottom I think you can solve for a critical point.

- anonymous

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- Venomblast

get the common denominator. so multiply cosx on the 1st term

- anonymous

thats it zep!!!!!!!!

- Venomblast

? zep?

- anonymous

@zepdrix :D

- Venomblast

i guess he/she got it from here

- zepdrix

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- anonymous

i think the top should be ignored

- anonymous

the book doesent have a mention of it

- anonymous

neither does the graph

- anonymous

the only root is 0

- anonymous

http://www.wolframalpha.com/input/?i=graph+xtanx

- anonymous

maybe it would matter if the interval was larger than -pi/2,pi/2

- zepdrix

yah fair enough c:

- zepdrix

Hmmm wait what was I saying?
cos x = 0
Hmm that should give you x = pi/2 right?
why did i say it was x = 0?
Hmmmmmmmmmmmmmmmmm
Now I'm back to being confused about where the 0 critical point is coming from :D lol

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