(-x)3+18x2-81x=0

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Solution for (-x)3+18x2-81x=0 equation:



(-x)3+18x^2-81x=0
We add all the numbers together, and all the variables
18x^2+(-1x)3-81x=0
We add all the numbers together, and all the variables
18x^2-81x+(-1x)3=0
We multiply parentheses
18x^2-81x-3x=0
We add all the numbers together, and all the variables
18x^2-84x=0
a = 18; b = -84; c = 0;
Δ = b2-4ac
Δ = -842-4·18·0
Δ = 7056
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{7056}=84$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-84)-84}{2*18}=\frac{0}{36} =0 $
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-84)+84}{2*18}=\frac{168}{36} =4+2/3 $

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