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महाराष्ट्र राज्य शिक्षण मंडळएचएससी विज्ञान (सामान्य) इयत्ता ११ वी

Answer the following: Show that z = (-1+-32)3 is a rational number

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प्रश्न

Answer the following:

Show that z = `((-1 + sqrt(-3))/2)^3` is a rational number

बेरीज
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उत्तर

`((-1 + sqrt(-3))/2)^3 = ((-1 + sqrt(3 xx - 1))/2)^3` 

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

= `(-1 + sqrt(3)"i")^3/8`

= `1/8[(-1)^3 + 3(-1)^2 sqrt(3)"i" + 3(-1)(sqrt(3)"i")^2 + (sqrt(3)"i")^3]`

= `1/8[-1 + 3sqrt(3)"i" - 3 xx 3"i"^2 + 3sqrt(3)"i"^3]`

= `1/8[-1 + 3sqrt(3)"i" + 9 - 3sqrt(3)"i"]`  ...[∵ i2 = – 1, i3 = – i]

= `1/8(8)`

= 1, which is a rational number.

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पाठ 1: Complex Numbers - Miscellaneous Exercise 1.2 [पृष्ठ २२]

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बालभारती Mathematics and Statistics (Arts and Science) Part 2 [English] Standard 11 Maharashtra State Board
पाठ 1 Complex Numbers
Miscellaneous Exercise 1.2 | Q II.14 | पृष्ठ २२

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