(9x+8)(9x+7)=0

Solution for (9x+8)(9x+7)=0 equation:

(9x+8)(9x+7)=0

We multiply parentheses ..

(+81x^2+63x+72x+56)=0

We get rid of parentheses

81x^2+63x+72x+56=0

We add all the numbers together, and all the variables

81x^2+135x+56=0

a = 81; b = 135; c = +56;
Δ = b2-4ac
Δ = 1352-4·81·56
Δ = 81
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{81}=9$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(135)-9}{2*81}=\frac{-144}{162}
=-8/9
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(135)+9}{2*81}=\frac{-126}{162}
=-7/9
$