(x+3)(4x-(5))=0

Solution for (x+3)(4x-(5))=0 equation:

(x+3)(4x-(5))=0

We multiply parentheses ..

(+4x^2-5x+12x-15)=0

We get rid of parentheses

4x^2-5x+12x-15=0

We add all the numbers together, and all the variables

4x^2+7x-15=0

a = 4; b = 7; c = -15;
Δ = b2-4ac
Δ = 72-4·4·(-15)
Δ = 289
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{289}=17$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(7)-17}{2*4}=\frac{-24}{8}
=-3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(7)+17}{2*4}=\frac{10}{8}
=1+1/4
$