3r^2+21r=0

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Solution for 3r^2+21r=0 equation: 



3r^2+21r=0

a = 3; b = 21; c = 0;
Δ = b2-4ac
Δ = 212-4·3·0
Δ = 441
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{441}=21$


$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-21}{2*3}=\frac{-42}{6}
=-7
$


$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+21}{2*3}=\frac{0}{6}
=0
$

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