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Solve: 0.05x^2.32> 4* 1.05^x-1?

Update:

4* 1.05^(x-1)

2 Answers

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  • Alan
    Lv 7
    4 years ago

    if you meant

    0.05*x^(2.32) > 4* 1.05^(x-1)

    === I believe the answer is

    x> 7.59508046

    === why

    multiple both sides by 20

    x^2.32 > 80* 1.05^(x-1)

    x^2.32 - 80* 1.05^(x-1)> 0

    so find the equal "= " case first,

    Then, you can try point above and below this point to determine the correct zone.

    y = x^2.32 - 80* 1.05^(x-1)

    so you are looking where y > 0 to meet the inequality.

    Using Newton Raphson Method

    graph the equation to show an area to guess

    (or just try points looking for 0 crossings )

    for example find f(7.4) and f(7.6)

    f(7.4) = -5.419984155

    f(7.6) = 0.139427036 , so 7.6 is greater than zero so it will be x> 7.XXXX

    so you know one answer for equal point is between 7.4 < x< 7.6

    Excel indicates for all negative values of x, the y are undefined.

    for real numbers

    and the only real answer about 7.5

    x> 7.5XXXX

    now just use newton raphson method to refine the answer

    next guess = prev guess - f(x)/f'(x)

    ng = pg - (x^2.32 - 80* 1.05^(x-1))/(2.32*(x^1.32) - 80*ln(1.05)*(1.05)^(x-1) )

    pg adjustment New Guess

    7.5 -0.095988095 7.595988095

    7.595988095 0.000907554 7.595080541

    7.595080541 8.13622E-08 7.59508046

    7.59508046 4.01327E-15 7.59508046

    7.59508046 -6.01991E-15 7.59508046

    so according to Excel

    x> 7.59508046

    Desmos graphing utilities also shows negative value of x, but

    everything I read tells me the graph is wrong.

    Every time I tried to use Newton Raphson method with this

    It says (-5.738)^(2.32) is undefined in real numbers

    .I know you cannnot have negative even roots. (-5)^(-1/2) is undefined.

    (-5)^(2.32) = (-5)^2*(-5)^(0.32)

  • 4 years ago

    Add brackets to show what the exponent of 1.05 is.

    Ex.

    (1.05^x) - 1 or 1.05^(x-1)

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