Then the depth of the wheat is increasing at the rate of
(A) 1 m/h
(B) 0 1 m/h
(C)  1 1 m/h
(D) 0 5 m/h
Summary
® If a quantity y varies with another quantity x, satisfying some rule 
( )
y
=f x
,
then dy
dx  (or 
f( )
′x
) represents the rate of change of y with respect to x and
0
x x
dy
dx
=
   
 (or 
( )0
′f x
) represents the  rate of change of y with respect to x at
0
x
=x