9m^2-66m+21=0

Solution for 9m^2-66m+21=0 equation:

9m^2-66m+21=0

a = 9; b = -66; c = +21;
Δ = b2-4ac
Δ = -662-4·9·21
Δ = 3600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$m_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$m_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3600}=60$
$m_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-66)-60}{2*9}=\frac{6}{18}
=1/3
$
$m_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-66)+60}{2*9}=\frac{126}{18}
=7
$