3x^2-21x-7=0

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Solution for 3x^2-21x-7=0 equation:



3x^2-21x-7=0
a = 3; b = -21; c = -7;
Δ = b2-4ac
Δ = -212-4·3·(-7)
Δ = 525
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:
$\sqrt{\Delta}=\sqrt{525}=\sqrt{25*21}=\sqrt{25}*\sqrt{21}=5\sqrt{21}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-5\sqrt{21}}{2*3}=\frac{21-5\sqrt{21}}{6} $
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+5\sqrt{21}}{2*3}=\frac{21+5\sqrt{21}}{6} $

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