If z1 = 1 + i and z2 = 2 - i, what is z1 * z2?
Answer and explanation
Correct answer: B. 3 + i
- Step 1: Expand using i^2 = -1: (a + bi)(c + di) = (ac - bd) + (ad + bc)i.
- Step 2: Real part: 2 - (-1) = 3; imaginary part: -1 + 2 = 1.
Answer
3 + i.
Why not the others: Typical slips are forgetting that i^2 = -1, multiplying real and imaginary parts only with each other, or flipping the sign of the imaginary part.
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