3x^2-9x=390

Solution for 3x^2-9x=390 equation:

3x^2-9x=390

We move all terms to the left:

3x^2-9x-(390)=0

a = 3; b = -9; c = -390;
Δ = b2-4ac
Δ = -92-4·3·(-390)
Δ = 4761
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{4761}=69$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-9)-69}{2*3}=\frac{-60}{6}
=-10
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-9)+69}{2*3}=\frac{78}{6}
=13
$