21x^2-79x+21=0

Solution for 21x^2-79x+21=0 equation:

21x^2-79x+21=0

a = 21; b = -79; c = +21;
Δ = b2-4ac
Δ = -792-4·21·21
Δ = 4477
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:

$\sqrt{\Delta}=\sqrt{4477}=\sqrt{121*37}=\sqrt{121}*\sqrt{37}=11\sqrt{37}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-79)-11\sqrt{37}}{2*21}=\frac{79-11\sqrt{37}}{42}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-79)+11\sqrt{37}}{2*21}=\frac{79+11\sqrt{37}}{42}
$