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Show that 1 + i10 + i20 + i30 is a real number

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Question

Show that 1 + i10 + i20 + i30 is a real number

Sum
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Solution

1 + i10 + i20 + i30 

= 1 + (i4)2.i2 + (i4)5 + (i4)7.i2

= 1 + (1)2 (–1) + (1)5 + (1)7 (–1)   ...[∵ i4 = 1, i2 = – 1]

= 1 – 1 + 1 – 1

= 0, which is a real number.

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Chapter 1: Complex Numbers - Exercise 1.1 [Page 6]

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