40=-0.004x^2+50

Solution for 40=-0.004x^2+50 equation:

40=-0.004x^2+50

We move all terms to the left:

40-(-0.004x^2+50)=0

We get rid of parentheses

0.004x^2-50+40=0

We add all the numbers together, and all the variables

0.004x^2-10=0

a = 0.004; b = 0; c = -10;
Δ = b2-4ac
Δ = 02-4·0.004·(-10)
Δ = 0.16
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{0.16}}{2*0.004}=\frac{0-\sqrt{0.16}}{0.008}
=-\frac{\sqrt{}}{0.008}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{0.16}}{2*0.004}=\frac{0+\sqrt{0.16}}{0.008}
=\frac{\sqrt{}}{0.008}
$