Does there exist a function which is continuous everywhere but not differentiable
at exactly two points Justify your answer 21 If 
( )
( )
( )
f x
g x
h x
y
l
m
n
a
b
c
=
, prove that 
( )
( )
( )
f
x
g x
h x
dy
l
m
n
dx
a
b
c
′
′
′
=
22