X(1.5x)=15

Solution for X(1.5x)=15 equation:

X(1.5X)=15

We move all terms to the left:

X(1.5X)-(15)=0

We add all the numbers together, and all the variables

X(+1.5X)-15=0

We multiply parentheses

X^2-15=0

a = 1; b = 0; c = -15;
Δ = b2-4ac
Δ = 02-4·1·(-15)
Δ = 60
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{60}=\sqrt{4*15}=\sqrt{4}*\sqrt{15}=2\sqrt{15}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{15}}{2*1}=\frac{0-2\sqrt{15}}{2}
=-\frac{2\sqrt{15}}{2}
=-\sqrt{15}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{15}}{2*1}=\frac{0+2\sqrt{15}}{2}
=\frac{2\sqrt{15}}{2}
=\sqrt{15}
$