y*y+2y=399

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Solution for y*y+2y=399 equation:



y*y+2y=399
We move all terms to the left:
y*y+2y-(399)=0
We add all the numbers together, and all the variables
2y+y*y-399=0
Wy multiply elements
y^2+2y-399=0
a = 1; b = 2; c = -399;
Δ = b2-4ac
Δ = 22-4·1·(-399)
Δ = 1600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1600}=40$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-40}{2*1}=\frac{-42}{2} =-21 $
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+40}{2*1}=\frac{38}{2} =19 $

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