3x(3x+1=21)

Solution for 3x(3x+1=21) equation:

3x(3x+1=21)

We move all terms to the left:

3x(3x+1-(21))=0

We add all the numbers together, and all the variables

3x(3x-20)=0

We multiply parentheses

9x^2-60x=0

a = 9; b = -60; c = 0;
Δ = b2-4ac
Δ = -602-4·9·0
Δ = 3600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3600}=60$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-60)-60}{2*9}=\frac{0}{18}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-60)+60}{2*9}=\frac{120}{18}
=6+2/3
$