x^2-21x=168

Solution for x^2-21x=168 equation:

x^2-21x=168

We move all terms to the left:

x^2-21x-(168)=0

a = 1; b = -21; c = -168;
Δ = b2-4ac
Δ = -212-4·1·(-168)
Δ = 1113
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-\sqrt{1113}}{2*1}=\frac{21-\sqrt{1113}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+\sqrt{1113}}{2*1}=\frac{21+\sqrt{1113}}{2}
$