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If a = -1+3i2, b = -1-3i2 then show that a2 = b and b2 = a

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Question

If a = `(-1 + sqrt(3)"i")/2`, b = `(-1 - sqrt(3)"i")/2` then show that a2 = b and b2 = a

Sum
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Solution

a = `(-1 + sqrt(3)"i")/2`, b = `(-1 - sqrt(3)"i")/2`

∴ a2 = `((-1 + sqrt(3)"i")/2)^2 = (1 - 2sqrt(3)"i" + 3"i"^2)/4`

= `(1 - 2sqrt(3)"i" + 3(-1))/4`   ...[∵ i2 = – 1]

= `(-2 - 2sqrt(3)"i")/4`

= `(-1 - sqrt(3)"i")/2` = b

and b2 = `((-1 - sqrt(3)"i")/2)^2 = (1 + 2sqrt(3)"i" + 3"i"^2)/4`

= `(1 + 2sqrt(3)"i" + 3(-1))/4`   . ...[∵ i2 = – 1]

= `(-2 + 2sqrt(3)"i")/4`

= `(-1 + sqrt(3)"i")/2` = a

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

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