-7(30-x)(x-10)=0

Solution for -7(30-x)(x-10)=0 equation:

-7(30-x)(x-10)=0

We add all the numbers together, and all the variables

-7(-1x+30)(x-10)=0

We multiply parentheses ..

-7(-1x^2+10x+30x-300)=0

We multiply parentheses

7x^2-70x-210x+2100=0

We add all the numbers together, and all the variables

7x^2-280x+2100=0

a = 7; b = -280; c = +2100;
Δ = b2-4ac
Δ = -2802-4·7·2100
Δ = 19600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{19600}=140$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-280)-140}{2*7}=\frac{140}{14}
=10
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-280)+140}{2*7}=\frac{420}{14}
=30
$