(x+10)(x+9)=16

Solution for (x+10)(x+9)=16 equation:

(x+10)(x+9)=16

We move all terms to the left:

(x+10)(x+9)-(16)=0

We multiply parentheses ..

(+x^2+9x+10x+90)-16=0

We get rid of parentheses

x^2+9x+10x+90-16=0

We add all the numbers together, and all the variables

x^2+19x+74=0

a = 1; b = 19; c = +74;
Δ = b2-4ac
Δ = 192-4·1·74
Δ = 65
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(19)-\sqrt{65}}{2*1}=\frac{-19-\sqrt{65}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(19)+\sqrt{65}}{2*1}=\frac{-19+\sqrt{65}}{2}
$