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

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

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

We add all the numbers together, and all the variables

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

We multiply parentheses ..

(-3y^2-1y+21y+7)=0

We get rid of parentheses

-3y^2-1y+21y+7=0

We add all the numbers together, and all the variables

-3y^2+20y+7=0

a = -3; b = 20; c = +7;
Δ = b2-4ac
Δ = 202-4·(-3)·7
Δ = 484
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{484}=22$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-22}{2*-3}=\frac{-42}{-6}
=+7
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+22}{2*-3}=\frac{2}{-6}
=-1/3
$