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Math Help - Use the Binomial Theorem to find the 3rd term of (4x+3y)^9

  1. #1
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    Use the Binomial Theorem to find the 3rd term of (4x+3y)^9

    My problem is that I'm going through a practice exam and my answer does not match any of the choices. Please help me to determine if my formula is incorrect. Thanks in advance!

    Use the Binomial Theorem to find the 3rd term of (4x+3y)^9

    3=2+1, thus k = 2, a = 4x, b = 3y, n = 9

    9!/(2!7!)*4x^7*3y^2

    My answer = 5308416x^7y^2

    However, the answers are:

    a) 419,894x^7y^2; b) 314,928x^7y^2, c) 419,904x^2y^8, or d) 1,259,712x^2y^7

    Please tell me what I'm doing wrong, I just don't get it...
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by lilrhino View Post
    My problem is that I'm going through a practice exam and my answer does not match any of the choices. Please help me to determine if my formula is incorrect. Thanks in advance!

    Use the Binomial Theorem to find the 3rd term of (4x+3y)^9

    3=2+1, thus k = 2, a = 4x, b = 3y, n = 9

    9!/(2!7!)*4x^7*3y^2

    My answer = 5308416x^7y^2

    However, the answers are:

    a) 419,894x^7y^2; b) 314,928x^7y^2, c) 419,904x^2y^8, or d) 1,259,712x^2y^7

    Please tell me what I'm doing wrong, I just don't get it...
    i actually got the same as you did

    let me try something else

    yes, you got the right answer, i don't know what happened, but either you or the book your looking out of made a typo somewhere. are you sure the signs are right place and everything?
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  3. #3
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    Quote Originally Posted by Jhevon View Post
    i actually got the same as you did

    let me try something else

    yes, you got the right answer, i don't know what happened, but either you or the book your looking out of made a typo somewhere. are you sure the signs are right and everything?
    Jhevon, I double-checked and it says to find the 3rd term of (4x+3y)^9

    Maybe it is a typo then...

    Thanks for your response .
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  4. #4
    Senior Member ecMathGeek's Avatar
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    Quote Originally Posted by Jhevon View Post
    i actually got the same as you did

    let me try something else

    yes, you got the right answer, i don't know what happened, but either you or the book your looking out of made a typo somewhere. are you sure the signs are right place and everything?
    Yeah. I don't see any way that any of those other solutions can be the correct one.
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