(x-3)(4x+5)=-15

Solution for (x-3)(4x+5)=-15 equation:

(x-3)(4x+5)=-15

We move all terms to the left:

(x-3)(4x+5)-(-15)=0

We add all the numbers together, and all the variables

(x-3)(4x+5)+15=0

We multiply parentheses ..

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

We get rid of parentheses

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

We add all the numbers together, and all the variables

4x^2-7x=0

a = 4; b = -7; c = 0;
Δ = b2-4ac
Δ = -72-4·4·0
Δ = 49
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{49}=7$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-7}{2*4}=\frac{0}{8}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+7}{2*4}=\frac{14}{8}
=1+3/4
$