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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, 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.

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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 roots of the equation xยณ = 1.

Step 2: We also know that ๐œ”ยณ = 1, so ๐œ”โด = ๐œ”, ๐œ”โต = ๐œ”ยฒ, ๐œ”โถ = 1, and so on. This means that we can express ๐œ”ยนโน and ๐œ”ยฒยณ in terms of ๐œ” and ๐œ”ยฒ.

Step 3: ๐œ”ยนโน = ๐œ”โถ3 + 1 = ๐œ”ยน = ๐œ” and ๐œ”ยฒยณ = ๐œ”โถ3 + 2 = ๐œ”ยฒ.

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

Step 5: This simplifies to [(2 โ€“ ๐œ”)ยฒ] [(2 โ€“ ๐œ”ยฒ)ยฒ].

Step 6: We know that 1 + ๐œ” + ๐œ”ยฒ = 0, so ๐œ”ยฒ = -1 - ๐œ” and ๐œ” = -1 - ๐œ”ยฒ.

Step 7: Substituting these values in, we get [(2 โ€“ (-1 - ๐œ”ยฒ))ยฒ] [(2 โ€“ (-1 - ๐œ”))ยฒ] = (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: Substituting ๐œ”โด = ๐œ” and ๐œ”ยฒ = -1 - ๐œ”, we get (9 + 6(-1 - ๐œ”) + ๐œ”) (9 + 6๐œ” - 1 - ๐œ”).

Step 10: Simplifying this, we get (8 - 5๐œ”) (8 + 5๐œ”).

Step 11: Finally, multiplying this out, we get 64 - 25๐œ”ยฒ.

Step 12: Substituting ๐œ”ยฒ = -1 - ๐œ”, we get 64 - 25(-1 - ๐œ”) = 64 + 25 + 25๐œ” = 89 + 25๐œ”.

Step 13: But we know that ๐œ” + 1 = -๐œ”ยฒ, so 89 + 25๐œ” = 89 - 25๐œ”ยฒ = 89 - 25(-1 - ๐œ”) = 89 + 25 + 25๐œ” = 114 + 25๐œ”.

Step 14: Repeating this process, we get 114 + 25(-1 - ๐œ”) = 114 - 25 - 25๐œ” = 89 - 25๐œ”.

Step 15: This process will continue indefinitely, so the expression does not simplify to a constant value. Therefore, the given statement is not true. The expression (2 โ€“ ๐œ”) (2 โ€“ ๐œ”ยฒ) (2 โ€“ ๐œ”ยนโน) (2 โ€“ ๐œ”ยฒยณ) does not equal 49.

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