3x(x-5)-3x*2=-30

Solution for 3x(x-5)-3x*2=-30 equation:

3x(x-5)-3x*2=-30

We move all terms to the left:

3x(x-5)-3x*2-(-30)=0

We add all the numbers together, and all the variables

3x(x-5)-3x*2+30=0

We multiply parentheses

3x^2-15x-3x*2+30=0

Wy multiply elements

3x^2-15x-6x+30=0

We add all the numbers together, and all the variables

3x^2-21x+30=0

a = 3; b = -21; c = +30;
Δ = b2-4ac
Δ = -212-4·3·30
Δ = 81
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{81}=9$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-9}{2*3}=\frac{12}{6}
=2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+9}{2*3}=\frac{30}{6}
=5
$