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

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

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

We add all the numbers together, and all the variables

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

We multiply parentheses ..

(+3u^2+9u+7u+21)=0

We get rid of parentheses

3u^2+9u+7u+21=0

We add all the numbers together, and all the variables

3u^2+16u+21=0

a = 3; b = 16; c = +21;
Δ = b2-4ac
Δ = 162-4·3·21
Δ = 4
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{4}=2$
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(16)-2}{2*3}=\frac{-18}{6}
=-3
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(16)+2}{2*3}=\frac{-14}{6}
=-2+1/3
$