X=60+-0.2x2

Solution for X=60+-0.2x2 equation:

X=60+-0.2X^2

We move all terms to the left:

X-(60+-0.2X^2)=0

We use the square of the difference formula

-(60-0.2X^2)+X=0

We get rid of parentheses

0.2X^2+X-60=0

a = 0.2; b = 1; c = -60;
Δ = b2-4ac
Δ = 12-4·0.2·(-60)
Δ = 49
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{49}=7$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(1)-7}{2*0.2}=\frac{-8}{0.4}
=-20
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+7}{2*0.2}=\frac{6}{0.4}
=15
$