3(y-7)(y+1)=0

Solution for 3(y-7)(y+1)=0 equation:

3(y-7)(y+1)=0

We multiply parentheses ..

3(+y^2+y-7y-7)=0

We multiply parentheses

3y^2+3y-21y-21=0

We add all the numbers together, and all the variables

3y^2-18y-21=0

a = 3; b = -18; c = -21;
Δ = b2-4ac
Δ = -182-4·3·(-21)
Δ = 576
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{576}=24$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-18)-24}{2*3}=\frac{-6}{6}
=-1
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-18)+24}{2*3}=\frac{42}{6}
=7
$