400=8p2

Solution for 400=8p2 equation:

400=8p^2

We move all terms to the left:

400-(8p^2)=0

a = -8; b = 0; c = +400;
Δ = b2-4ac
Δ = 02-4·(-8)·400
Δ = 12800
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$p_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$p_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{12800}=\sqrt{6400*2}=\sqrt{6400}*\sqrt{2}=80\sqrt{2}$
$p_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-80\sqrt{2}}{2*-8}=\frac{0-80\sqrt{2}}{-16}
=-\frac{80\sqrt{2}}{-16}
=-\frac{5\sqrt{2}}{-1}
$
$p_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+80\sqrt{2}}{2*-8}=\frac{0+80\sqrt{2}}{-16}
=\frac{80\sqrt{2}}{-16}
=\frac{5\sqrt{2}}{-1}
$