#4) Sum of 2 Angles
var('y')
show(cos(x+y))
show(cos(x+y).simplify_trig())
show(plot3d(cos(x+y),(x,-2,2),(y,-2,2)),viewer='tachyon')
show(plot3d(cos(x)*cos(y)-sin(x)*sin(y),(x,-2,2),(y,-2,2)),viewer='tachyon')
#5) Sum of 2 Angles
var('y')
show(cos(x-y))
show(cos(x-y).simplify_trig())
show(plot3d(cos(x-y),(x,-2,2),(y,-2,2)),viewer='tachyon')
show(plot3d(cos(x)*cos(y)+sin(x)*sin(y),(x,-2,2),(y,-2,2)),viewer='tachyon')