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

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

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

We multiply parentheses ..

(+7x^2-49x+8x-56)=0

We get rid of parentheses

7x^2-49x+8x-56=0

We add all the numbers together, and all the variables

7x^2-41x-56=0

a = 7; b = -41; c = -56;
Δ = b2-4ac
Δ = -412-4·7·(-56)
Δ = 3249
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3249}=57$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-41)-57}{2*7}=\frac{-16}{14}
=-1+1/7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-41)+57}{2*7}=\frac{98}{14}
=7
$