2. 2.2 The Derivative of a
Function
The derivative of a function f given by y = f (x) with
respect to x at any x in its domain is the number:
β π¦
β π₯
= lim
Ξπ₯β0
π π₯ + Ξπ₯ β π π₯
Ξπ₯
Other notations for
β π¦
β π₯
are βΆ fβ²(x), yβ²
To avoid confusion, let us denote our Ξx to h.
β π¦
β π₯
= lim
ββ0
π π₯ + β β π π₯
β
We will be using this formula by definition of the
derivative.
6. DIFFERENTATION
RULES
There are standard
formulas called
differentiation formulas or
differentiation rules which
will enable us to find the
derivative of even
complicated functions as
rapidly as we can write.
7. ο§ Rule 1: The Constant
Rule
If f(x) = c where c is constant, then fβ(x) = 0. The derivative of a constant is just
equal to zero.
β
β π₯
(c) = 0
EXAMPLE 1 : y = 5
EXAMPLE 2:
EXAMPLE 3: y = 5Ο
EXAMPLE 4:
y = 1000
=
β
β π₯
(1000)
yβ = 0
y = π
=
β
β π₯
( π)
yβ = 0
=
β
β π₯
(5)
yβ = 0
=
β
β π₯
(5Ο)
yβ = 0
DiFFERENTiATiON
RULES
8. ο§ Rule 2: The Power Rule
If f(x) = π₯π, then fβ (x) = nπ₯πβ1
β
β π₯
(π₯π
) = nπ₯πβ1
EXAMPLE 1: =
β
β π₯
(π₯4)
EXAMPLE 3: y = π
EXAMPLE 2: y = π₯6
EXAMPLE 4: y =
1
π₯2
y = π₯4
yβ = 4 π₯4β1
yβ = 4 π₯3
yβ = (6) π₯6β1
yβ = 6 π₯5
=
β
β π₯
( π₯6)
= (π₯)
1
2 = π₯β2
yβ = β2π₯βπ
yβ =
π
π
(π₯)
1
2
β1
=
π
π
(π₯)β
1
2
yβ =
1
2 π₯
1
2
=
1
2 π₯
yβ = β2π₯β2β1
or =
β2
π₯3
DiFFERENTiATiON
RULES
9. ο§ Rule 3: The Identity Function
Rule
DiFFERENTiATiON
RULES
β
β π₯
(x) = 1
If f(x) = x where x is not raised to any power, then fβ(x) = 1. The derivative of x is
always 1.
EXAMPLE 1 : y = x
=
β
β π₯
(x)
= 1
10. ο§ Rule 4: The Constant Multiple Rule
EXAMPLE 1 : y = 5π₯8
EXAMPLE 2 :
EXAMPLE 3 : y = 4π₯3
y =
1
4
π₯8
yβ = 8 5π₯8β1
yβ = 3 4π₯3β1
β
β π₯
(c f (x) = c fβ (x))
. .
yβ = 40π₯7
yβ = 12π₯2
yβ = 8
1
4
π₯8β1
yβ = 2π₯7
If f(x) = c f (x), where c is constant, then fβ (x) = c fβ (x)
. .
DiFFERENTiATiON
RULES
11. ο§ Rule 5: The Sum/Difference Rule
EXAMPLE 1 : y = 5x + 3
EXAMPLE 2 :
EXAMPLE 3 : y = 4π₯3 β ππ
y = πππ
+ πππ
yβ = π π + π yβ = 3 4π₯3β1 β π(π)
β
β π₯
(f(x)Β±g(x))= fβ(x) Β±gβ²(x)
yβ = π yβ = 12π₯2 β π
yβ = π ππ₯πβ1
+ π
yβ = 6π
DiFFERENTiATiON
RULES