X^2+18x-28=0

Solution for X^2+18x-28=0 equation:

X^2+18X-28=0

a = 1; b = 18; c = -28;
Δ = b2-4ac
Δ = 182-4·1·(-28)
Δ = 436
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:

$\sqrt{\Delta}=\sqrt{436}=\sqrt{4*109}=\sqrt{4}*\sqrt{109}=2\sqrt{109}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(18)-2\sqrt{109}}{2*1}=\frac{-18-2\sqrt{109}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(18)+2\sqrt{109}}{2*1}=\frac{-18+2\sqrt{109}}{2}
$