the function is one of the form y=g(x) +cosbx. find two linear functions y1 and y2 related to g such that y1 is less than or equal to y is less than or equal to y2.
a. y= 2x + cos x
b. y= 1-0.5x+ cos2x
since -1 <= cosx <= 1
(a) 2x-1 <= y <= 2x+1
(b) 1-.05x-1 <= y <= 1-.05x+1
or, -.05x <= y <= 2-.05x
visit
http://rechneronline.de/function-graphs/
and play around some to see