-15x^2+28-5=0

Solution for -15x^2+28-5=0 equation:

-15x^2+28-5=0

We add all the numbers together, and all the variables

-15x^2+23=0

a = -15; b = 0; c = +23;
Δ = b2-4ac
Δ = 02-4·(-15)·23
Δ = 1380
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:

$\sqrt{\Delta}=\sqrt{1380}=\sqrt{4*345}=\sqrt{4}*\sqrt{345}=2\sqrt{345}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{345}}{2*-15}=\frac{0-2\sqrt{345}}{-30}
=-\frac{2\sqrt{345}}{-30}
=-\frac{\sqrt{345}}{-15}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{345}}{2*-15}=\frac{0+2\sqrt{345}}{-30}
=\frac{2\sqrt{345}}{-30}
=\frac{\sqrt{345}}{-15}
$