3x(-2x-7)=15

Solution for 3x(-2x-7)=15 equation:

3x(-2x-7)=15

We move all terms to the left:

3x(-2x-7)-(15)=0

We multiply parentheses

-6x^2-21x-15=0

a = -6; b = -21; c = -15;
Δ = b2-4ac
Δ = -212-4·(-6)·(-15)
Δ = 81
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{81}=9$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-9}{2*-6}=\frac{12}{-12}
=-1$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+9}{2*-6}=\frac{30}{-12}
=-2+1/2$