21x^2-60x+39=0

Solution for 21x^2-60x+39=0 equation:

21x^2-60x+39=0

a = 21; b = -60; c = +39;
Δ = b2-4ac
Δ = -602-4·21·39
Δ = 324
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{324}=18$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-60)-18}{2*21}=\frac{42}{42}
=1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-60)+18}{2*21}=\frac{78}{42}
=1+6/7
$