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

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

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

We move all terms to the left:

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

We add all the numbers together, and all the variables

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

We multiply parentheses

4x^2-3x+12x-15=0

We add all the numbers together, and all the variables

4x^2+9x-15=0

a = 4; b = 9; c = -15;
Δ = b2-4ac
Δ = 92-4·4·(-15)
Δ = 321
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(9)-\sqrt{321}}{2*4}=\frac{-9-\sqrt{321}}{8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+\sqrt{321}}{2*4}=\frac{-9+\sqrt{321}}{8}
$