15=10*x2

Solution for 15=10*x2 equation:

15=10x^2

We move all terms to the left:

15-(10x^2)=0

a = -10; b = 0; c = +15;
Δ = b2-4ac
Δ = 02-4·(-10)·15
Δ = 600
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:

$\sqrt{\Delta}=\sqrt{600}=\sqrt{100*6}=\sqrt{100}*\sqrt{6}=10\sqrt{6}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-10\sqrt{6}}{2*-10}=\frac{0-10\sqrt{6}}{-20}
=-\frac{10\sqrt{6}}{-20}
=-\frac{\sqrt{6}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+10\sqrt{6}}{2*-10}=\frac{0+10\sqrt{6}}{-20}
=\frac{10\sqrt{6}}{-20}
=\frac{\sqrt{6}}{-2}
$