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Find the value of: x3 – 3x2 + 19x – 20, if x = 1 – 4i

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प्रश्न

Find the value of: x3 – 3x2 + 19x – 20, if x = 1 – 4i

योग
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उत्तर

x = 1 – 4i

∴ x – 1 = – 4i

∴ (x – 1)2 = 16i2

∴ x2 – 2x + 1 = – 16      ...[∵ i2 = – 1]

∴ x2 – 2x + 17 = 0        ...(i)

                       x – 1
`x^2 – 2x + 17")"overline(x^3 - 3x^2 + 19x - 20)"`
                        x3 – 2x2 + 17x
                        –      +       –              
                              –  x2 + 2x  – 20
                              –  x2 + 2x – 17x
                              –      +       –         
                                               –  3

∴ x3 – 3x2 + 19x – 20

= (x2 – 2x + 17) (x – 1) – 3  

= 0(x – 1) – 3                  ...[From (i)]

= 0 – 3

∴ x3 – 3x2 + 19x – 20 = – 3 

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अध्याय 3: Complex Numbers - MISCELLANEOUS EXERCISE - 3 [पृष्ठ ४३]

APPEARS IN

बालभारती Mathematics and Statistics (Commerce) Part 1 [English] Standard 11 Maharashtra State Board
अध्याय 3 Complex Numbers
MISCELLANEOUS EXERCISE - 3 | Q 5) iii) | पृष्ठ ४३

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