(5b+10)(b-9)=0

Solution for (5b+10)(b-9)=0 equation:

(5b+10)(b-9)=0

We multiply parentheses ..

(+5b^2-45b+10b-90)=0

We get rid of parentheses

5b^2-45b+10b-90=0

We add all the numbers together, and all the variables

5b^2-35b-90=0

a = 5; b = -35; c = -90;
Δ = b2-4ac
Δ = -352-4·5·(-90)
Δ = 3025
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3025}=55$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-35)-55}{2*5}=\frac{-20}{10}
=-2
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-35)+55}{2*5}=\frac{90}{10}
=9
$