Quadratic Equations
Complex Roots
Grade 11

Question:

<p>Solve the equation <span class="math">\((1 + i)x^2 + (1 - i)x - 2i = 0\)</span> and find <span class="math">\(|\alpha - \beta|^2\)</span> where <span class="math">\(\alpha, \beta\)</span> are the roots.</p>

Step-by-Step Solution

Key Concept: Use Vieta's formulas to find sum and product of roots, then compute the difference using the discriminant formula.
<p><strong>Step 1:</strong> Divide the equation by <span class="math">$(1+i)$</span>:</p><p><span class="math">$$x^2 + \frac{(1-i)}{(1+i)}x - \frac{2i}{(1+i)} = 0$$</span></p><p><strong>Step 2:</strong> Simplify to get <span class="math">$x^2 - ix - (1+i) = 0$</span></p><p><strong>Step 3:</strong> By Vieta's formulas: <span class="math">$\alpha + \beta = i$</span> and <span class="math">$\alpha\beta = -(1+i)$</span></p><p><strong>Step 4:</strong> Calculate <span class="math">$\alpha - \beta = \sqrt{(\alpha+\beta)^2 - 4\alpha\beta} = \sqrt{i^2 + 4(1+i)} = \sqrt{-1+4+4i} = \sqrt{3+4i}$</span></p><p><strong>Step 5:</strong> <span class="math">$|\alpha - \beta| = \sqrt{9+16} = 5$</span></p><p><strong>Step 6:</strong> Therefore <span class="math">$|\alpha - \beta|^2 = 5$</span></p><p>∴ Answer is <strong>5</strong>.</p>
Correct Answer: 5

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