cos5pie/4 -sin3pie/4=
( 5pie/4 = 225 degree, and 3pie/4 = 135 degree )
cos 225 - sin135 =
cos ( 180 + 45 ) - sin ( 90 + 45) =
cos( 180 + 45 ) = - cos45 , and sin ( 90 + 45) = cos 45 ⇒
- cos 45 - cos45 =
- 2cos45 =
cos 45=sqrt2/2 ⇒
- 2* sqrt2/2 =
- sqrt2