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    Can someone please help me find the integral of:

    1/(5+3cosx)

    Thanks.
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    try a t-substitution
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    (Original post by around)
    try a t-substitution
    :eek:
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    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.
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    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.
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    (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
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    Have you tried the t-substitution?
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    (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:

    \displaystyle\int \dfrac{\sec^2\dfrac{\pi}{2}}{8+2  \tan^2\dfrac{\pi}{2}}
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    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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