/pi \ /pi \ cos|-- + y|*sin|-- + y| \4 / \4 /
cos(pi/4 + y)*sin(pi/4 + y)
/pi + 4*y\ /pi + 4*y\ cos|--------|*sin|--------| \ 4 / \ 4 /
cos(2*y) -------- 2
/ ___ ___ \ / ___ ___ \ |\/ 2 *cos(y) \/ 2 *sin(y)| |\/ 2 *cos(y) \/ 2 *sin(y)| |------------ + ------------|*|------------ - ------------| \ 2 2 / \ 2 2 /