SOLUTION: f(x)= -2x^3-2x find x if f(x) =-49

Question 204837: f(x)= -2x^3-2x find x if f(x) =-49
Found 2 solutions by checkley77, RAY100:
Answer by checkley77(12844) (Show Source): You can put this solution on YOUR website!
f(x)=-2x^3-2x
find x if f(x)=-49
f(-49)=-2(-49^3)-2*-49
f(-49)=-2*-117,649+98
f(-49)=235,298+98
f(-49)=235,396 ans.

Answer by RAY100(1637) (Show Source): You can put this solution on YOUR website!
With deference to my esteemed college..perhaps we should try
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f(x) = -2x^3 -2x =-49,,,when x=?
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or -2x^3 -2x +49 =0,,,,solve for x.
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In general this is a negative cubic function.
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On the x-y coordinate system, this drops from top left to bottom right, with 2 (3-1) turns, and normally 3 answers.
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Normally we would factor the function, to find the zero's.
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However after much work, we plotted the function and found that two of the zeros are imaginary. The function does drop and does turn twice, but it only crosses the x axis once, hence 2 imaginary Zeros (3-1=2)
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The x intercept is at about (2.789, 0)
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checking: substitute in original function
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-2(2.789)^3 -2(2.789) =49 ,,,,,,ok
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Have a great weekend

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