Define a polynomial equation. z 2 + A z + ( 2 5 + 3 0 i ) = z 1 2 5 i
Let w 1 , w 2 and w 3 be the roots of the equation above. ( w 1 , w 2 , w 3 ∈ C )
If A ∈ C makes the equation ∣ w 1 ∣ = ∣ w 2 ∣ = ∣ w 3 ∣ to be true.
Find the value of ∣ ∣ ∣ ∣ w 1 ∣ 3 ( w 3 ) − 1 w 3 ⋅ w 3 w 2 + ∣ w 2 ∣ 3 ( w 1 ) − 1 w 1 ⋅ w 1 w 3 + ∣ w 3 ∣ 3 ( w 2 ) − 1 w 2 ⋅ w 2 w 1 ∣ ∣ ∣ 2 .
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Change the term. ∣ w 1 ∣ 3 ( w 3 ) − 1 w 3 ⋅ w 3 w 2 → ∣ w 3 ∣ 3 w 3 w 3 ⋅ w 3 w 2 , As we know that for any complex number k , k k = ∣ k ∣ 2
We can change the term through these steps. ∣ w 3 ∣ 3 w 3 w 3 ⋅ w 3 w 2 → ∣ w 3 ∣ 3 ∣ w 3 ∣ 2 ⋅ w 3 w 2 → ∣ w 3 ∣ w 3 w 2
Do those steps to the other two and we will get this as the result. ∣ ∣ ∣ ∣ ∣ ∣ w 1 ∣ 3 ( w 3 ) − 1 w 3 ⋅ w 3 w 2 + ∣ w 2 ∣ 3 ( w 1 ) − 1 w 1 ⋅ w 1 w 3 + ∣ w 3 ∣ 3 ( w 2 ) − 1 w 2 ⋅ w 2 w 1 ∣ ∣ ∣ ∣ ∣ 2 = ∣ ∣ ∣ ∣ ∣ w 3 ∣ w 3 w 2 + ∣ w 1 ∣ w 1 w 3 + ∣ w 2 ∣ w 2 w 1 ∣ ∣ ∣ ∣ 2
Again, consider the fact that ∣ w 1 ∣ = ∣ w 2 ∣ = ∣ w 3 ∣ ∣ ∣ ∣ ∣ ∣ w 3 ∣ w 3 w 2 + ∣ w 1 ∣ w 1 w 3 + ∣ w 2 ∣ w 2 w 1 ∣ ∣ ∣ ∣ 2 → ∣ ∣ ∣ ∣ ∣ w 1 ∣ w 3 w 2 + ∣ w 1 ∣ w 1 w 3 + ∣ w 1 ∣ w 2 w 1 ∣ ∣ ∣ ∣ 2 → ∣ ∣ ∣ ∣ ∣ w 1 ∣ w 3 w 2 + w 1 w 3 + w 2 w 1 ∣ ∣ ∣ ∣ 2 → ∣ w 1 ∣ 2 ∣ w 3 w 2 + w 1 w 3 + w 2 w 1 ∣ 2
Multiply by z both sides. z 2 + A z + ( 2 5 + 3 0 i ) = z 1 2 5 i → z 3 + A z 2 + ( 2 5 + 3 0 i ) z − 1 2 5 i = 0
From the Vieta's formular. We know that. w 1 w 2 + w 2 w 3 + w 3 w 1 = 2 5 + 3 0 i w 1 w 2 w 3 = 1 2 5 i
Take the absolute both sides. ∣ w 1 w 2 + w 2 w 3 + w 3 w 1 ∣ = ∣ 2 5 + 3 0 i ∣ → ∣ w 1 w 2 + w 2 w 3 + w 3 w 1 ∣ 2 = 1 5 2 5 a n d ∣ w 1 w 2 w 3 ∣ = ∣ 1 2 5 i ∣ → ∣ w 1 ∣ 3 = 1 2 5 → ∣ w 1 ∣ 2 = 2 5
Plug in the value. ∣ w 1 ∣ 2 ∣ w 3 w 2 + w 1 w 3 + w 2 w 1 ∣ 2 = ∣ w 1 ∣ 2 ∣ w 1 w 2 + w 2 w 3 + w 3 w 1 ∣ 2 = 2 5 1 5 2 5 = 6 1