Hi, I need help finding the sin of the angle alpha in standard postion whose terminal side contains the given point. (-4,-6).

Here's what I have so far.

r = sqrt{(-4)^2 + (-6)^2} = sqrt{52}

x = -4, y= -6, r= sqrt{52}

sin(alpha) = (-6/sqrt(52))

= (-6/sqrt(52)*sqrt(52)/sqrt(52)

=-6(sqrt(13*2*2) / 52)

The answer ends up being sin(alpha)= {3(sqrt(13)/13}

And that is where I am getting lost... It's simpler algebra that I should already know, but I just don't remember. Here's an image that might be easier on the eyes...

The box is around the answer I should get to. Thanks for any help.