Example 24
Determine the concavity of f (x) = cos x + sin
x on [0, 2p] and identify any points
of inflection.
Solution : f (x) = cos x +
sin x and x Î [0,
2p]
Also, f ’ (x) = cos x  sin x and
f " (x) =  sin x  cos x
Now f " (x) = 0
Þ 
sin x = cos x
\ tan x = 1
\ x =
,
Î [0,
2p]
[next page]
