-0.08x^2+8.2x=2.1x+3.5

Solution for -0.08x^2+8.2x=2.1x+3.5 equation:

-0.08x^2+8.2x=2.1x+3.5

We move all terms to the left:

-0.08x^2+8.2x-(2.1x+3.5)=0

We get rid of parentheses

-0.08x^2+8.2x-2.1x-3.5=0

We add all the numbers together, and all the variables

-0.08x^2+6.1x-3.5=0

a = -0.08; b = 6.1; c = -3.5;
Δ = b2-4ac
Δ = 6.12-4·(-0.08)·(-3.5)
Δ = 36.09
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{-(6.1)-\sqrt{36.09}}{2*-0.08}=\frac{-6.1-\sqrt{36.09}}{-0.16}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(6.1)+\sqrt{36.09}}{2*-0.08}=\frac{-6.1+\sqrt{36.09}}{-0.16}
$