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

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

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

We add all the numbers together, and all the variables

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

We multiply parentheses ..

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

We get rid of parentheses

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

We add all the numbers together, and all the variables

-4u^2+25u+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:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

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