3(a-8)(a+1)=0

Solution for 3(a-8)(a+1)=0 equation:

3(a-8)(a+1)=0

We multiply parentheses ..

3(+a^2+a-8a-8)=0

We multiply parentheses

3a^2+3a-24a-24=0

We add all the numbers together, and all the variables

3a^2-21a-24=0

a = 3; b = -21; c = -24;
Δ = b2-4ac
Δ = -212-4·3·(-24)
Δ = 729
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

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