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    lkjs's Avatar
    lkjs Posts: 3, Reputation: 1
    New Member
     
    #1

    Nov 14, 2009, 03:16 AM
    compound angles
    hey how to you solve this problem:

    find exact value of cosec(5pi/12):
    this is what I did

    = 1 / sin( pi/4 + pi/6 )
    = 1 / ( sin( pi/4)cos( pi/6 ) + cos( pi/4 )sin( pi/6) )
    = 1 / ( (√3/(2√2) )+( (1/(2√2)) )
    = 1 / ( (√3+1) / 2√2)

    then rationalised and got end answer as 4 / (√6 + √2)

    but the answer in the book come as just √6 + √2

    Help would be kindly appreciated.
    galactus's Avatar
    galactus Posts: 2,271, Reputation: 282
    Ultra Member
     
    #2

    Nov 14, 2009, 05:20 AM
    You are correct.

    If the book has , then that is incorrect.
    s_cianci's Avatar
    s_cianci Posts: 5,472, Reputation: 760
    Uber Member
     
    #3

    Nov 14, 2009, 07:55 AM
    I actually get √6 - √2 when I do it. If you rationalize your denominator in
    4 / (√6 + √2) you'll see it.
    Unknown008's Avatar
    Unknown008 Posts: 8,076, Reputation: 723
    Uber Member
     
    #4

    Nov 14, 2009, 07:56 AM

    Strange, I'm getting ... :confused:

    From
    Unknown008's Avatar
    Unknown008 Posts: 8,076, Reputation: 723
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    #5

    Nov 14, 2009, 07:57 AM
    Quote Originally Posted by s_cianci View Post
    I actually get √6 - √2 when I do it. If you rationalize your denominator in
    4 / (√6 + √2) you'll see it.
    Lol, a minute difference! :p

    Those LaTeX codes sure take some time.

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