0=u^2+7u-8

Solution for 0=u^2+7u-8 equation:

0=u^2+7u-8

We move all terms to the left:

0-(u^2+7u-8)=0

We add all the numbers together, and all the variables

-(u^2+7u-8)=0

We get rid of parentheses

-u^2-7u+8=0

We add all the numbers together, and all the variables

-1u^2-7u+8=0

a = -1; b = -7; c = +8;
Δ = b2-4ac
Δ = -72-4·(-1)·8
Δ = 81
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{81}=9$
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-9}{2*-1}=\frac{-2}{-2}
=1
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+9}{2*-1}=\frac{16}{-2}
=-8
$