12x^2-21x-90=0

Solution for 12x^2-21x-90=0 equation:

12x^2-21x-90=0

a = 12; b = -21; c = -90;
Δ = b2-4ac
Δ = -212-4·12·(-90)
Δ = 4761
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{4761}=69$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-69}{2*12}=\frac{-48}{24}
=-2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+69}{2*12}=\frac{90}{24}
=3+3/4
$