(5+u)(5u-4)=0

Solution for (5+u)(5u-4)=0 equation:

(5+u)(5u-4)=0

We add all the numbers together, and all the variables

(u+5)(5u-4)=0

We multiply parentheses ..

(+5u^2-4u+25u-20)=0

We get rid of parentheses

5u^2-4u+25u-20=0

We add all the numbers together, and all the variables

5u^2+21u-20=0

a = 5; b = 21; c = -20;
Δ = b2-4ac
Δ = 212-4·5·(-20)
Δ = 841
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{841}=29$
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-29}{2*5}=\frac{-50}{10}
=-5
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+29}{2*5}=\frac{8}{10}
=4/5
$