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# Integral of Trig Function watch

1/(5+3cosx)

Thanks.
2. try a t-substitution
3. (Original post by around)
try a t-substitution
4. Assuming you don't know what it is:

http://en.wikipedia.org/wiki/Tangent_half-angle_formula

Basically, you introduce a new variable t, where t=tan(x/2) in this case. You can write cos x in terms of tan (x/2), and hence in terms of t, and then just substitute normally.
5. Be aware that by normal A-level standards, this is a very hard question - and pretty much impossible if you've not seen the t=tan x/2 substitution before.
6. (Original post by DFranklin)
Be aware that by normal A-level standards, this is a very hard question - and pretty much impossible if you've not seen the t=tan x/2 substitution before.
Well I'm at uni so haha. And still can't do it
7. Have you tried the t-substitution?
8. (Original post by DFranklin)
Have you tried the t-substitution?
Yes. But I'm stuck with secs and tans and dont know what to do with them.

I've gotten to a dead end:

9. Huh? Where do the pi/2's come from? Post your full working. (You only have to go to the point after you've done the substitution).

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Updated: February 1, 2010
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