(4u+7)(9-u)=0

Solution for (4u+7)(9-u)=0 equation:

(4u+7)(9-u)=0

We add all the numbers together, and all the variables

(4u+7)(-1u+9)=0

We multiply parentheses ..

(-4u^2+36u-7u+63)=0

We get rid of parentheses

-4u^2+36u-7u+63=0

We add all the numbers together, and all the variables

-4u^2+29u+63=0

a = -4; b = 29; c = +63;
Δ = b2-4ac
Δ = 292-4·(-4)·63
Δ = 1849
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1849}=43$
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(29)-43}{2*-4}=\frac{-72}{-8}
=+9
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(29)+43}{2*-4}=\frac{14}{-8}
=-1+3/4
$