(8x+7)(x-3)=0

Solution for (8x+7)(x-3)=0 equation:

(8x+7)(x-3)=0

We multiply parentheses ..

(+8x^2-24x+7x-21)=0

We get rid of parentheses

8x^2-24x+7x-21=0

We add all the numbers together, and all the variables

8x^2-17x-21=0

a = 8; b = -17; c = -21;
Δ = b2-4ac
Δ = -172-4·8·(-21)
Δ = 961
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{961}=31$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-17)-31}{2*8}=\frac{-14}{16}
=-7/8
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-17)+31}{2*8}=\frac{48}{16}
=3
$