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    c) α = 5, β = -¾

    Use the method shown in the above example to write down the equations whose roots are: (α+β and αβ)

    I get...
    α+β= 5/4
    αβ= -15/4

     x^2 + \frac{5}{4}x - \frac{15}{4}x = 0 ((times by 4 to remove the fractions))
     4x^2 + 5x - 15 = 0

    The answer is
    4x2 -17x - 15 = 0

    What did I do wrong?
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    (Original post by ckfeister)
    c) α = 5, β = -¾

    Use the method shown in the above example to write down the equations whose roots are: (α+β and αβ)

    I get...
    α+β= 5/4
    αβ= -15/4

     x^2 + \frac{5}{4}x - \frac{15}{4}x = 0 ((times by 4 to remove the fractions))
     4x^2 + 5x - 15 = 0

    The answer is
    4x2 -17x - 15 = 0

    What did I do wrong?
    \displaystyle \alpha + \beta \neq \frac{5}{4}
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    On the next question,
    α = -3, β = -4

    I get

    α+β= -7
    αβ= 12


     x^2 - 7x + 12 = 0

    The answer is
    x2 + 7x + 12 = 0

    What did I do wrong here?
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    (Original post by Mr M)
    \displaystyle \alpha + \beta \neq \frac{5}{4}
    Nevermind, what about the above?
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    (Original post by ckfeister)
    How do I do  \alpha + \beta = then?
    Type in \displaystyle 5-\frac{3}{4} into your calculator?
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    (Original post by Mr M)
    Type in \displaystyle 5-\frac{3}{4} into your calculator?
    I noticed after looking at it, I have dyslexic so I can't find these on own for some reason... also what about the other question? I got -7x not +7x (question is above)
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    (Original post by ckfeister)
    what about the other question? I got -7x not +7x (question is above)
    This is the third time you have had the same problem at this final step on different threads so I don't think you are getting it. You always need to change the sign of the sum.

    It's because \alpha + \beta = -\frac{b}{a} (note the negative sign).
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    (Original post by Mr M)
    This is the third time you have had the same problem at this final step on different threads so I don't think you are getting it. You always need to change the sign of the sum.

    It's because \alpha + \beta = -\frac{b}{a} (note the negative sign).
    So even when shown on  \alpha + \beta I still use negative sign? I know  - \frac{b}{a}
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    (Original post by ckfeister)
    So even when shown on  \alpha + \beta I still use negative sign? I know  - \frac{b}{a}
    To form the quadratic equation do this:

    x^2 - (sum of roots) x + (product of roots) =0

    This will always give you the right answer.
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    (Original post by Mr M)
    To form the quadratic equation do this:

    x^2 - (sum of roots) x + (product of roots) =0

    This will always give you the right answer.
    thx
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    P = FV
    Answer is ( 31 )
    ( -93 1/2 )

    How comes I got -42 1/2 on bottom?
    (27*-2) + (5*17) = 31
    (0*-2) + (-5 1/2*17) = -42.5
    ??

    Name:  fp11.jpg
Views: 17
Size:  276.6 KB
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    (Original post by ckfeister)
    P = FV
    Answer is ( 31 )
    ( -93 1/2 )

    How comes I got -42 1/2 on bottom?
    (27*-2) + (5*17) = 31
    (0*-2) + (-5 1/2*17) = -42.5
    ??

    Name:  fp11.jpg
Views: 17
Size:  276.6 KB
    It's your dyslexia again. You have read a five as a two.
    • Thread Starter
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    (Original post by Mr M)
    It's your dyslexia again. You have read a five as a two.
    Nevermind found it, thx again...
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    (Original post by ckfeister)
    Where?
    Negative five point five times seventeen.
 
 
 
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