21x=4x2

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Solution for 21x=4x2 equation:



21x=4x^2
We move all terms to the left:
21x-(4x^2)=0
determiningTheFunctionDomain -4x^2+21x=0
a = -4; b = 21; c = 0;
Δ = b2-4ac
Δ = 212-4·(-4)·0
Δ = 441
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{441}=21$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-21}{2*-4}=\frac{-42}{-8} =5+1/4 $
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+21}{2*-4}=\frac{0}{-8} =0 $

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