0=10.5-0.4x^2

Solution for 0=10.5-0.4x^2 equation:

0=10.5-0.4x^2

We move all terms to the left:

0-(10.5-0.4x^2)=0

We add all the numbers together, and all the variables

-(10.5-0.4x^2)=0

We get rid of parentheses

0.4x^2-10.5=0

a = 0.4; b = 0; c = -10.5;
Δ = b2-4ac
Δ = 02-4·0.4·(-10.5)
Δ = 16.8
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{-(0)-\sqrt{16.8}}{2*0.4}=\frac{0-\sqrt{16.8}}{0.8}
=-\frac{\sqrt{}}{0.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{16.8}}{2*0.4}=\frac{0+\sqrt{16.8}}{0.8}
=\frac{\sqrt{}}{0.8}
$