As written there is an infinite number of "solutions" in the form of (x,y)(x,y)pairs for which the equation is valid, including: (0,6), (1,5), (-2,2)(0,6),(1,5),(−2,2), etc.
I will assume you wanted the solution for the x intercept, which is equivalent to the solution to
color(white)("XXXX")XXXX0 = -x^2+60=−x2+6
color(white)("XXXX")XXXXcolor(white)("XXXX")XXXX(if this is not the case, re-post your question with clarification)
If -x^2+6 = 0−x2+6=0
then, equivalently,
color(white)("XXXX")XXXXx^2-6 = 0x2−6=0
color(white)("XXXX")XXXXx^2 = 6x2=6
color(white)("XXXX")XXXX(x+0)^2 = 6(x+0)2=6color(white)("XXXX")XXXXwould technically "complete the square... but to what point?
color(white)("XXXX")XXXX(x+0) = +-sqrt(6)(x+0)=±√6color(white)("XXXX")XXXXcarrying on as if it were necessary
color(white)("XXXX")XXXXx = +-sqrt6x=±√6