(7x-2)(x+4)=0

Solution for (7x-2)(x+4)=0 equation:

(7x-2)(x+4)=0

We multiply parentheses ..

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

We get rid of parentheses

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

We add all the numbers together, and all the variables

7x^2+26x-8=0

a = 7; b = 26; c = -8;
Δ = b2-4ac
Δ = 262-4·7·(-8)
Δ = 900
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{900}=30$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(26)-30}{2*7}=\frac{-56}{14}
=-4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(26)+30}{2*7}=\frac{4}{14}
=2/7
$