(4y+7)(8-y)=0

Solution for (4y+7)(8-y)=0 equation:

(4y+7)(8-y)=0

We add all the numbers together, and all the variables

(4y+7)(-1y+8)=0

We multiply parentheses ..

(-4y^2+32y-7y+56)=0

We get rid of parentheses

-4y^2+32y-7y+56=0

We add all the numbers together, and all the variables

-4y^2+25y+56=0

a = -4; b = 25; c = +56;
Δ = b2-4ac
Δ = 252-4·(-4)·56
Δ = 1521
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1521}=39$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(25)-39}{2*-4}=\frac{-64}{-8}
=+8
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(25)+39}{2*-4}=\frac{14}{-8}
=-1+3/4
$