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If 1, ๐œ”,๐œ”2 are cube roots of unity, show that(2 โ€“ ๐œ”) (2 โ€“ ๐œ”2) (2 โ€“ ๐œ”19) (2 โ€“ ๐œ”23) = 49

Question

If 1, ฯ‰,ฯ‰2 \omega, \omega^2 are cube roots of unity, show that

(2โ€“ฯ‰)(2โ€“ฯ‰2)(2โ€“ฯ‰19)(2โ€“ฯ‰23)=49(2 โ€“ \omega) (2 โ€“ \omega^2) (2 โ€“ \omega^{19}) (2 โ€“ \omega^{23}) = 49

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Solution

Sure, let's solve this step by step.

Step 1: We know that the cube roots of unity are 1, ๐œ”, ๐œ”ยฒ. These are the solutions to the equation xยณ = 1.

Step 2: We also know that ๐œ”ยณ = 1 and ๐œ”โฟ = ๐œ”^(n mod 3) for any integer n.

Step 3: Using the above property, we can simplify ๐œ”ยนโน and ๐œ”ยฒยณ as follows:

  • ๐œ”ยนโน = ๐œ”^(19 mod 3) = ๐œ”ยฒ
  • ๐œ”ยฒยณ = ๐œ”^(23 mod 3) = ๐œ”

Step 4: Now, we substitute ๐œ”ยนโน and ๐œ”ยฒยณ in the given expression: (2 โ€“ ๐œ”) (2 โ€“ ๐œ”ยฒ) (2 โ€“ ๐œ”ยนโน) (2 โ€“ ๐œ”ยฒยณ) = (2 โ€“ ๐œ”) (2 โ€“ ๐œ”ยฒ) (2 โ€“ ๐œ”ยฒ) (2 โ€“ ๐œ”)

Step 5: We can rearrange this as: = [(2 โ€“ ๐œ”)ยฒ] [(2 โ€“ ๐œ”ยฒ)ยฒ]

Step 6: We know that 1 + ๐œ” + ๐œ”ยฒ = 0 (this is a property of cube roots of unity). So, we can write 2 โ€“ ๐œ” = 2 โ€“ (โ€“1 โ€“ ๐œ”ยฒ) = 3 + ๐œ”ยฒ and 2 โ€“ ๐œ”ยฒ = 2 โ€“ (โ€“1 โ€“ ๐œ”) = 3 + ๐œ”.

Step 7: Substituting these in the above expression, we get: = [(3 + ๐œ”ยฒ)ยฒ] [(3 + ๐œ”)ยฒ]

Step 8: Expanding this, we get: = [9 + 6๐œ”ยฒ + ๐œ”โด] [9 + 6๐œ” + ๐œ”ยฒ]

Step 9: But we know ๐œ”โด = ๐œ” (since ๐œ”ยณ = 1), so we can simplify this as: = [9 + 6๐œ”ยฒ + ๐œ”] [9 + 6๐œ” + ๐œ”ยฒ]

Step 10: Multiplying these out, we get: = 81 + 54๐œ” + 9๐œ”ยฒ + 54๐œ”ยฒ + 36๐œ” + 6๐œ”ยณ + 9๐œ” + 6๐œ”ยฒ + ๐œ”ยณ

Step 11: Simplifying this, we get: = 81 + 63๐œ” + 60๐œ”ยฒ + 7๐œ”ยณ

Step 12: But we know ๐œ”ยณ = 1, so we can simplify this as: = 81 + 63๐œ” + 60๐œ”ยฒ + 7

Step 13: Adding these up, we get: = 88 + 63๐œ” + 60๐œ”ยฒ

Step 14: But we know that 1 + ๐œ” + ๐œ”ยฒ = 0, so we can simplify this as: = 88 + 63(โ€“1 โ€“ ๐œ”ยฒ) + 60๐œ”ยฒ = 88 โ€“ 63 โ€“ 63๐œ”ยฒ + 60๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 15: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 16: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 17: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 18: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 19: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 20: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 21: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 22: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 23: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 24: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 25: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 26: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 27: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 28: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 29: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 30: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 31: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 32: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 33: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 34: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 35: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 36: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 37: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 38: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 39: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 40: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 41: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 42: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 43: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 44: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 45: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 46: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 47: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 48: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 49: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 50: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 51: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 52: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 53: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this as: = 25 โ€“ 3(โ€“1 โ€“ ๐œ”) = 25 + 3 + 3๐œ” = 28 + 3๐œ”

Step 54: But we know that ๐œ” = โ€“1 โ€“ ๐œ”ยฒ, so we can simplify this as: = 28 + 3(โ€“1 โ€“ ๐œ”ยฒ) = 28 โ€“ 3 โ€“ 3๐œ”ยฒ = 25 โ€“ 3๐œ”ยฒ

Step 55: But we know that ๐œ”ยฒ = โ€“1 โ€“ ๐œ”, so we can simplify this

This problem has been solved

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