-4x^2-21x+18=0

Solution for -4x^2-21x+18=0 equation:

-4x^2-21x+18=0

a = -4; b = -21; c = +18;
Δ = b2-4ac
Δ = -212-4·(-4)·18
Δ = 729
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{729}=27$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-27}{2*-4}=\frac{-6}{-8}
=3/4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+27}{2*-4}=\frac{48}{-8}
=-6
$