4r^2-12r-135=0

Solution for 4r^2-12r-135=0 equation:

4r^2-12r-135=0

a = 4; b = -12; c = -135;
Δ = b2-4ac
Δ = -122-4·4·(-135)
Δ = 2304
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2304}=48$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-12)-48}{2*4}=\frac{-36}{8}
=-4+1/2
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-12)+48}{2*4}=\frac{60}{8}
=7+1/2
$