e f(x2) > f (x1)
Thus, we have
1
2
1
2
1
2
(
)
(
), for all
,
[ , ]
x
x
f x
f x
x x
a b
<
 
 
 
 
 
Hence, f  is an increasing function in [a,b] The proofs of part (b) and (c) are similar It is left as an exercise to the reader