3(x2-21)=20x

Solution for 3(x2-21)=20x equation:

3(x2-21)=20x

We move all terms to the left:

3(x2-21)-(20x)=0

We add all the numbers together, and all the variables

3(+x^2-21)-20x=0

We multiply parentheses

3x^2-20x-63=0

a = 3; b = -20; c = -63;
Δ = b2-4ac
Δ = -202-4·3·(-63)
Δ = 1156
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1156}=34$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-34}{2*3}=\frac{-14}{6}
=-2+1/3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+34}{2*3}=\frac{54}{6}
=9
$