If α > 1 > |w1| and |w1|² + |w2|² + α² = |w1|² + α²|w2|², where w1 and w2 are complex numbers and α is a real number, then

Question image

Understand the Problem

The question is asking us to evaluate the relationship between the complex numbers and their moduli under the conditions given. We need to find out which of the four provided statements about the moduli of the complex numbers is true based on the equation presented.

Answer

$|w_2| = \alpha$.
Answer for screen readers

The correct answer is: B. $|w_2| = \alpha$.

Steps to Solve

  1. Understand the Given Equation

We have the equation: $$ |w_1|^2 |w_2|^2 + \alpha^2 = |w_1|^2 + \alpha^2 |w_2|^2 $$

  1. Rearrange the Equation

Let's rearrange this equation to isolate terms related to the moduli. We subtract $|w_1|^2$ from both sides: $$ |w_1|^2 |w_2|^2 - |w_1|^2 + \alpha^2 - \alpha^2 |w_2|^2 = 0 $$

  1. Factor the Expression

Now, we can factor the first two terms: $$ |w_1|^2 (|w_2|^2 - 1) + \alpha^2 (1 - |w_2|^2) = 0 $$

  1. Set the Expression to Zero

For the equation to hold true, the two terms must sum to zero. This leads us to two possible cases:

  • Case 1: $|w_2|^2 = 1$
  • Case 2: $|w_1|^2 = 0$
  1. Analyze the Cases

If $|w_2|^2 = 1$, then $|w_2| = 1$. If $|w_1|^2 = 0$, it means $|w_1| = 0$.

Given that $\alpha > 1 > |w_1|$, we find that:

  • $|w_2|$ must relate to $\alpha$ while satisfying $|w_2| \leq \alpha$.
  1. Check the Options

Now, we check the provided answer choices against the findings:

  • Option A: $|w_1| = 1$ (incorrect because $|w_1| < 1$)
  • Option B: $|w_2| = \alpha$ (could be true)
  • Option C: $|w_1| = 1 + \alpha$ (incorrect, as $|w_1| < 1$)
  • Option D: $|w_2| = 1$ (could be true but conflicts with given conditions on $\alpha$)

The correct answer is: B. $|w_2| = \alpha$.

More Information

The condition requires $|w_1| < 1$ and $\alpha > 1$, indicating that $|w_2|$ can be equal to $\alpha$ under these constraints. The relationship amongst $|w_1|$, $|w_2|$, and $\alpha$ reveals that while $|w_2|$ might be equal to $\alpha$, it cannot exceed it due to the conditions established.

Tips

  • Assuming both $|w_1|$ and $|w_2|$ can be greater than $\alpha$.
  • Misinterpreting the inequality condition on $|w_1|$. It's crucial to remember $|w_1| < 1$.

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