De-Moiver's Theorem: Complex Number
LIKE TO JOIN ON FACEBOOK (click here)
De-Moiver's Theorem:-
has q distinct values and one of these is equal to
.
, where k = 0,1,2,3..........,n - 1
, where k = 0,1,2,3
, where k = 0,1,2,3 ........ , n - 1
=
De-Moiver's Theorem:-
if
then,
CASE 1st: If n is an integer then,
CASE 2nd: If n is a rational number ( different from integers)
i.e. n = p/q where p,q belong to integers,
and p,q have no common divisor then
Steps of root finding of a complex number 'z' :
Step 1: Convert 'z' into the 'Polar form' where
is the Principal value of the arg.z.
i.e. 
Step 2: Generalise
,
i.e.
, k belongs to integers
Step 3: The nth roots are given by,
or, 
Ques: Find the 4th roos of
?
Sol:
Step 1: Convert
into polar form.
if z = x + iy and we want to convert it into polar form then we have to multiply and divide the sum of square of x and y.
therefore, 
or, 
Step 2: Generalize the 
therefore, 
Step 3: The 4th roots are given by,
When , k = 0
similarly we can find the other roots i.e. 
NOTE:
For nth roots:
or,
, where k = 0,1,2,3 ........ , n - 1
for k = 0, 
k = 1, 
or, 
k = 2, 
..........................................................
..........................................................
......................................................
k = n - 1, 
1. All these roots are in G.P. with common ratio of 
2. All these roots lie on a circle of radius
whose centre is at the Origin.
3. All these roots are the vertices of a Regular Polygon of n-sides
or, 
or, 
or,
, where k = 0, 1, 2
or,
, k = 0, 1 ,2
a) Sum of the roots are zero when the modulus of the roots is unity.
i.e.
or, 
if
then 
therefore,
b) Product of the roots of the unity = 1 when n is an odd number.
i.e. 
Comments
Post a Comment