x*1.15x=210

Solution for x*1.15x=210 equation:

x*1.15x=210

We move all terms to the left:

x*1.15x-(210)=0

Wy multiply elements

x^2-210=0

a = 1; b = 0; c = -210;
Δ = b2-4ac
Δ = 02-4·1·(-210)
Δ = 840
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:

$\sqrt{\Delta}=\sqrt{840}=\sqrt{4*210}=\sqrt{4}*\sqrt{210}=2\sqrt{210}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{210}}{2*1}=\frac{0-2\sqrt{210}}{2}
=-\frac{2\sqrt{210}}{2}
=-\sqrt{210}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{210}}{2*1}=\frac{0+2\sqrt{210}}{2}
=\frac{2\sqrt{210}}{2}
=\sqrt{210}
$