(x+4)(8x+7)=0

Solution for (x+4)(8x+7)=0 equation:

(x+4)(8x+7)=0

We multiply parentheses ..

(+8x^2+7x+32x+28)=0

We get rid of parentheses

8x^2+7x+32x+28=0

We add all the numbers together, and all the variables

8x^2+39x+28=0

a = 8; b = 39; c = +28;
Δ = b2-4ac
Δ = 392-4·8·28
Δ = 625
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{625}=25$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(39)-25}{2*8}=\frac{-64}{16}
=-4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(39)+25}{2*8}=\frac{-14}{16}
=-7/8
$