x^2-21*x+104=0

Solution for x^2-21*x+104=0 equation:

x^2-21x+104=0

a = 1; b = -21; c = +104;
Δ = b2-4ac
Δ = -212-4·1·104
Δ = 25
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{25}=5$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-5}{2*1}=\frac{16}{2}
=8
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+5}{2*1}=\frac{26}{2}
=13
$