Question: 'Find the equation of the lines from point $P(0,6)$ tangent to the circle $x^2+y^2=4x+4$.
So what I did firstly is rewrite it to the form $(x-2)^2 + y^2 = 8$, and I saw that point $P$ is not on the circle. I learned that the equation of the line tangent to the circle $x^2+y^2=r^2$ from the point $P(a,b)$ is $xa+yb=r^2$
$ xa+yb=4x+4$
$x.o+y.6=2x+2.0 +4$ (This is the step I don't understand)
$6y=2x+4$
$y=\dfrac{1}{3}x + \dfrac{2}{3}$
So basically, my question is: Why did the $4x+4$ change into the $2x+4$?