10x-3x(-x+80)=400

Solution for 10x-3x(-x+80)=400 equation:

10x-3x(-x+80)=400

We move all terms to the left:

10x-3x(-x+80)-(400)=0

We add all the numbers together, and all the variables

10x-3x(-1x+80)-400=0

We multiply parentheses

3x^2+10x-240x-400=0

We add all the numbers together, and all the variables

3x^2-230x-400=0

a = 3; b = -230; c = -400;
Δ = b2-4ac
Δ = -2302-4·3·(-400)
Δ = 57700
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{57700}=\sqrt{100*577}=\sqrt{100}*\sqrt{577}=10\sqrt{577}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-230)-10\sqrt{577}}{2*3}=\frac{230-10\sqrt{577}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-230)+10\sqrt{577}}{2*3}=\frac{230+10\sqrt{577}}{6}
$