Orthogonality theorem proof method question

[SELFMADE]

can't figure out how that underlined segment transforms into whats at the bottom:

http://img7.imageshack.us/img7/9493/imag0254p.jpg

[Stephen Tashi]

It relies on
||x||^2 = x^T x
||y||^2 = y^T y
(-x^T y - y^T x) = -x^T y - x^Ty = -2 x^T y