40=0.45x^2

Solution for 40=0.45x^2 equation:

40=0.45x^2

We move all terms to the left:

40-(0.45x^2)=0

We get rid of parentheses

-0.45x^2+40=0

a = -0.45; b = 0; c = +40;
Δ = b2-4ac
Δ = 02-4·(-0.45)·40
Δ = 72
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{72}=\sqrt{36*2}=\sqrt{36}*\sqrt{2}=6\sqrt{2}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-6\sqrt{2}}{2*-0.45}=\frac{0-6\sqrt{2}}{-0.9}
=-\frac{6\sqrt{2}}{-0.9}
=-\frac{\sqrt{2}}{-0.15}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+6\sqrt{2}}{2*-0.45}=\frac{0+6\sqrt{2}}{-0.9}
=\frac{6\sqrt{2}}{-0.9}
=\frac{\sqrt{2}}{-0.15}
$