a2-22a+21=0

Solution for a2-22a+21=0 equation:

a2-22a+21=0

We add all the numbers together, and all the variables

a^2-22a+21=0

a = 1; b = -22; c = +21;
Δ = b2-4ac
Δ = -222-4·1·21
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-22)-20}{2*1}=\frac{2}{2}
=1
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-22)+20}{2*1}=\frac{42}{2}
=21
$