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

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

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

We add all the numbers together, and all the variables

(+15x)(x-3)=0

We multiply parentheses ..

(+15x^2-45x)=0

We get rid of parentheses

15x^2-45x=0

a = 15; b = -45; c = 0;
Δ = b2-4ac
Δ = -452-4·15·0
Δ = 2025
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2025}=45$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-45)-45}{2*15}=\frac{0}{30}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-45)+45}{2*15}=\frac{90}{30}
=3
$