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

Solution for (3-u)(4u+7)=0 equation:

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

We add all the numbers together, and all the variables

(-1u+3)(4u+7)=0

We multiply parentheses ..

(-4u^2-7u+12u+21)=0

We get rid of parentheses

-4u^2-7u+12u+21=0

We add all the numbers together, and all the variables

-4u^2+5u+21=0

a = -4; b = 5; c = +21;
Δ = b2-4ac
Δ = 52-4·(-4)·21
Δ = 361
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{361}=19$
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(5)-19}{2*-4}=\frac{-24}{-8}
=+3
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(5)+19}{2*-4}=\frac{14}{-8}
=-1+3/4
$