x2+9x=-15

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Solution for x2+9x=-15 equation:



x2+9x=-15
We move all terms to the left:
x2+9x-(-15)=0
We add all the numbers together, and all the variables
x^2+9x+15=0
a = 1; b = 9; c = +15;
Δ = b2-4ac
Δ = 92-4·1·15
Δ = 21
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(9)-\sqrt{21}}{2*1}=\frac{-9-\sqrt{21}}{2} $
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+\sqrt{21}}{2*1}=\frac{-9+\sqrt{21}}{2} $

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