Answer
The error was that the constant was not subtracted from both sides before solving the equation.
Work Step by Step
$x(x-2)=8$
$x*x+x*-2=8$
$x^2-2x=8$
$x^2-2x-8=8-8$
$x^2-2x-8=0$
$(x-4)(x+2)=0$
$x-4=0$
$x-4+4=0+4$
$x=4$
$x+2=0$
$x+2-2=0-2$
$x=-2$
$x=-2, 4$
