8x^2-140=280

Solution for 8x^2-140=280 equation:

8x^2-140=280

We move all terms to the left:

8x^2-140-(280)=0

We add all the numbers together, and all the variables

8x^2-420=0

a = 8; b = 0; c = -420;
Δ = b2-4ac
Δ = 02-4·8·(-420)
Δ = 13440
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:

$\sqrt{\Delta}=\sqrt{13440}=\sqrt{64*210}=\sqrt{64}*\sqrt{210}=8\sqrt{210}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-8\sqrt{210}}{2*8}=\frac{0-8\sqrt{210}}{16}
=-\frac{8\sqrt{210}}{16}
=-\frac{\sqrt{210}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+8\sqrt{210}}{2*8}=\frac{0+8\sqrt{210}}{16}
=\frac{8\sqrt{210}}{16}
=\frac{\sqrt{210}}{2}
$