10x(2.1+x)=100

Solution for 10x(2.1+x)=100 equation:

10x(2.1+x)=100

We move all terms to the left:

10x(2.1+x)-(100)=0

We add all the numbers together, and all the variables

10x(x+2.1)-100=0

We multiply parentheses

10x^2+21x-100=0

a = 10; b = 21; c = -100;
Δ = b2-4ac
Δ = 212-4·10·(-100)
Δ = 4441
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-\sqrt{4441}}{2*10}=\frac{-21-\sqrt{4441}}{20}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+\sqrt{4441}}{2*10}=\frac{-21+\sqrt{4441}}{20}
$