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# Show that the Roots of X5 =1 Can Be Written as 1, α 1 , α 2 , α 3 , α 4 .Hence Show that ( 1 − α 1 ) ( 1 − α 2 ) ( 1 − α 3 ) ( 1 − α 4 ) = 5 . - Applied Mathematics 1

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ConceptPowers and Roots of Trigonometric Functions

#### Question

Show that the roots of x5 =1 can be written as 1, alpha^1,alpha^2,alpha^3,alpha^4 .hence show that (1-alpha^1) (1-alpha^2) (1-alpha^3)(1-alpha^4)=5.

#### Solution

x^5=1=cos0+i sin0

thereforex^5=cos(2kpi)+i sin(2kpi)

therefore x^1=(cos(2kpi)+i sin(2kpi))^(1/5)=cos((2kpi)/5)+i sin ((2kpi)/5)

Putting k=0,1,2,3,4 we get the five roots as

x_0=cos0+i sin0=1,

x_1=cos ((2pi)/5)+isin((2pi)/5),

x_2=cos((4pi)/5)+isin((4pi)/5),

x_3=cos((6pi)/5)+isin((6pi)/5),

x_4=cos((8pi)/5)+isin((8pi)/5).

Putting x_1=cos((2pi)/5)+isin((2pi)/5)=alpha we see that x_2=alpha^2, x_3=alpha^3, x_4=alpha^4

∴ the roots are 1, alpha, alpha^2, alpha^3, alpha^4 and hence

therefore x^5-1=(x-1)(x-alpha)(x-alpha^2)(x-alpha^3)(x-alpha^4)

therefore (x^5-1)/(x-1)=(x-alpha)(x-alpha^2)(x-alpha^3)(x-alpha^4)

therefore (x-alpha)(x-alpha^2)(x-alpha^3)(x-alpha^4)=x^4+x^3+x^2+x^1+1.

Putting x = 1, we get

(1-alpha)(1-alpha^2)(1-alpha^3)(1-alpha^4)=5

Is there an error in this question or solution?

#### APPEARS IN

Solution Show that the Roots of X5 =1 Can Be Written as 1, α 1 , α 2 , α 3 , α 4 .Hence Show that ( 1 − α 1 ) ( 1 − α 2 ) ( 1 − α 3 ) ( 1 − α 4 ) = 5 . Concept: Powers and Roots of Trigonometric Functions.
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