x2-15x=18

Solution for x2-15x=18 equation:

x2-15x=18

We move all terms to the left:

x2-15x-(18)=0

We add all the numbers together, and all the variables

x^2-15x-18=0

a = 1; b = -15; c = -18;
Δ = b2-4ac
Δ = -152-4·1·(-18)
Δ = 297
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:

$\sqrt{\Delta}=\sqrt{297}=\sqrt{9*33}=\sqrt{9}*\sqrt{33}=3\sqrt{33}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-3\sqrt{33}}{2*1}=\frac{15-3\sqrt{33}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+3\sqrt{33}}{2*1}=\frac{15+3\sqrt{33}}{2}
$