-0.10x^2-5x+840=0

Solution for -0.10x^2-5x+840=0 equation:

-0.10x^2-5x+840=0

We add all the numbers together, and all the variables

-0.1x^2-5x+840=0

a = -0.1; b = -5; c = +840;
Δ = b2-4ac
Δ = -52-4·(-0.1)·840
Δ = 361
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{361}=19$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-5)-19}{2*-0.1}=\frac{-14}{-0.2}
=+70
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-5)+19}{2*-0.1}=\frac{24}{-0.2}
=-120
$