1. NUMBERS
We already know that
πππ½ = ππ¨π¬ π½ + π πππ π½
πβππ½ = πππ π½ β π πππ π½
From the above two equations we have
ππ¨π¬ π½ =
πππ½ + πβππ½
π
& π¬π’π§ π½ =
πππ½ β πβππ½
ππ
These forms are known as Eulerβs exponential forms of circular functions.
Further, if z is a complex number we define
πππ π =
πππ
+ πβππ
π
& πππ π =
πππ
β πβππ
ππ
2. HYPERBOLIC FUNCTIONS
If x is real or complex
ππ+πβπ
π
is called hyperbolic cosine of x and is denoted
by cosh x and
ππβπβπ
π
is called hyperbolic sine of x and is denoted by sinh x.
Thus, ππππ π =
ππβπβπ
π
, ππππ π =
ππ+πβπ
π
Relationship between hyperbolic and circular functions:
(i) sin ix = i sinh x and sinh x = -i sin ix
(ii) cos ix = cosh x
(iii) tan ix = i tanh x and tanh x = -i tan ix
(iv) sinh ix = i sin x and sin x = -i sinh ix
(v) cosh ix = cos x
(vi) tanh ix = i tan x and tan x = -i tanh ix
8. INVERSE HYPERBOLIC FUNCTIONS
Definition: if sinh u = z then u is called inverse hyperbolic sine of z and is denoted
by π = ππππβππ.
Similarly we can define inverse hyperbolic cosine and inverse hyperbolic tangent
and other functions which we denote as ππππβππ, ππππβππ, πππ.
The inverse hyperbolic functions are many valued but we will consider their
principal values only.
If Z is real we can show that
1. ππππβππ = πππ π + ππ + π
2. ππππβπ
π = πππ π + ππ β π
3. ππππβπ
π =
π
π
πππ
π+π
πβπ
.
13. PROBLEMS BASED ON HYPERBOLIC FUNCTIONS
3. Solve the equation ππ
+ ππ
+ ππ
+ π = π
Roots of a Complex Number: De Moivreβs Theorem can be used to find all n-
roots of a complex number.
Since, πππ π½ = πππ πππ + π½ & πππ π½ = πππ (πππ + π½) where k is an integer.
We have by DeMoivreβs Theorem
πππ π½ + ππππ π½
π
π = πππ πππ + π½ + πππ (πππ + π½)
π
π
πππ π½ + ππππ π½
π
π = πππ
ππ π + π½
π
+ ππππ
ππ π + π½
π
By putting π = π, π, π, β¦ β¦ . . π β π we get n roots of the complex number.