4=6-x^2

4 = 6 - (x^2)

subtract

4 - 6 = -(x^2)

simplify

-2 = -(x^2)

divide by (-1)

2 = (x^2)

square root

sqrt(2) = sqrt(x^2)

simplify

$${\sqrt{}}$$$$\mathrm{\ }$$2 = x

then x = the square root of 2 or ~1.422....

almost :)

$$x=\pm\sqrt{2}$$