brackets generally express multiplication. a(b) would mean a times b. in this case, x is found to be a common factor in x^2 and 8x. by factorisation (removal of a common factor in this case), you get 2 factors for the original equation.

*look at example in picture*
here, c is a common factor in ac and bc, so we can remove the c to get (2)
if we were to multiply c and (a+b) again, we would get the original equation (1)

since at least one of the factors have to be zero for the product to be 0, c=0 or (a+b)=0