5=-16x^2+405

Solution for 5=-16x^2+405 equation:

5=-16x^2+405

We move all terms to the left:

5-(-16x^2+405)=0

We get rid of parentheses

16x^2-405+5=0

We add all the numbers together, and all the variables

16x^2-400=0

a = 16; b = 0; c = -400;
Δ = b2-4ac
Δ = 02-4·16·(-400)
Δ = 25600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{25600}=160$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-160}{2*16}=\frac{-160}{32}
=-5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+160}{2*16}=\frac{160}{32}
=5
$