## Calle87 3 years ago Need some help identifying the increase intervals of the graph of xtanx

1. Calle87

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2. Venomblast

is this in radian?

3. Calle87

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

4. Calle87

just wondering how to show the intervals of increase and decrease

5. Venomblast

so -90 degrees <x<90 degrees

6. Calle87

usually i take f'x and solve for 0

7. Venomblast

i see

8. Venomblast

i see no 0. is this is an equation?

9. Calle87

f'x=tanx+xsec^2x

10. Calle87

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

11. Calle87

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12. Calle87

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

13. Calle87

because when i set my derivative = 0 i have problems

14. zepdrix

|dw:1349988578994:dw| Hmm yah this derivative does seem to be putting up a fight :\ Hmmmmm

15. Calle87

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

16. zepdrix

|dw:1349988855254:dw| 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.

17. Calle87

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18. Venomblast

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

19. Calle87

thats it zep!!!!!!!!

20. Venomblast

? zep?

21. Calle87

@zepdrix :D

22. Venomblast

i guess he/she got it from here

23. zepdrix

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24. Calle87

i think the top should be ignored

25. Calle87

the book doesent have a mention of it

26. Calle87

neither does the graph

27. Calle87

the only root is 0

28. Calle87
29. Calle87

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

30. zepdrix

yah fair enough c:

31. 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