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Question
Express the following in the form of a + ib, a, b ∈ R, i = `sqrt(-1)`. State the values of a and b:
(1 + 2i)(– 2 + i)
Solution
(1 + 2i)(– 2 + i) = – 2 + i – 4i + 2i2
= – 2 – 3i + 2( – 1) ...[∵ i2 = – 1]
∴ (1 + 2i)(– 2 + i) = – 4 – 3i
∴ a = – 4 and b = – 3
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