-9x2-21x-6=0

Solution for -9x2-21x-6=0 equation:

-9x^2-21x-6=0

a = -9; b = -21; c = -6;
Δ = b2-4ac
Δ = -212-4·(-9)·(-6)
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-15}{2*-9}=\frac{6}{-18}
=-1/3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+15}{2*-9}=\frac{36}{-18}
=-2
$