® If two variables x and y are varying with respect to another variable t, i e , if
( )
x
=f t
and 
( )
y
=g t
, then by Chain Rule
dy
dy
dx
dt
dt
dx =
,  if  
0
dx
dt ≠ ® A function  f  is said to be
(a) increasing on an interval (a, b) if
x1 < x2  in (a, b) ⇒ f (x1) < f (x2) for all x1, x2 ∈ (a, b)