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Let ω be a nonreal root of z3=1. Let a1,a2,,an be real numbers such that 1a1+ω+1a2+ω++1an+ω=2+5i.Compute 2a11a21a1+1+2a21a22a2+1++2an1a2nan+1.

 Jun 12, 2019
edited by LeoIsTheBest  Jun 13, 2019
edited by LeoIsTheBest  Jun 13, 2019

Best Answer 

 #7
avatar
+1

ω=12±i32.

Consider a general term on the lhs,

 1ak+ω=1(ak1/2)±i3/2=1(ak1/2)±i3/2.(ak1/2)i3/2(ak1/2)±i3/2

 

=(ak1/2)i3/2(ak1/2)2+3/4=(ak1/2)i3/2a2kak+1.

 

Substitute and equate reals,

a11/2a21a1+1+a21/2a22a2+1++an1/2a2nan+1=2,

and multiplying that by 2,

2a11a21a1+1+2a21a22a2+1++2an1a2nan+1=4.

 Jun 13, 2019
edited by Guest  Jun 13, 2019
 #1
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+1

Can anybody read this question?

 Jun 13, 2019
 #2
avatar+24 
-4

nope

ProffesorNobody  Jun 13, 2019
 #3
avatar+24 
-4

maybe this helps: 

Letωbeanonrealrootofz3=1.Leta1,a2,,anberealnumberssuchthat\[1a1+ω+1a2+ω++1an+ω=2+5i.\]Compute\[2a11a21a1+1+2a21a22a2+1++2an1a2nan+1.\]

ProffesorNobody  Jun 13, 2019
 #4
avatar+24 
-4

actually it doesn't help...

ProffesorNobody  Jun 13, 2019
 #5
avatar+24 
-4

ok wow i can read it now..... but im confused now

 Jun 13, 2019
 #6
avatar+142 
0

I fixed it now.

 Jun 13, 2019
 #7
avatar
+1
Best Answer

ω=12±i32.

Consider a general term on the lhs,

 1ak+ω=1(ak1/2)±i3/2=1(ak1/2)±i3/2.(ak1/2)i3/2(ak1/2)±i3/2

 

=(ak1/2)i3/2(ak1/2)2+3/4=(ak1/2)i3/2a2kak+1.

 

Substitute and equate reals,

a11/2a21a1+1+a21/2a22a2+1++an1/2a2nan+1=2,

and multiplying that by 2,

2a11a21a1+1+2a21a22a2+1++2an1a2nan+1=4.

Guest Jun 13, 2019
edited by Guest  Jun 13, 2019

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