21d2-7d=0

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Solution for 21d2-7d=0 equation: 



21d^2-7d=0

a = 21; b = -7; c = 0;
Δ = b2-4ac
Δ = -72-4·21·0
Δ = 49
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{49}=7$


$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-7}{2*21}=\frac{0}{42}
=0
$


$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+7}{2*21}=\frac{14}{42}
=1/3
$

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