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]
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