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If (x + iy)3 = u + iv, then show that ux+vy =4(x2-y2) - Mathematics

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प्रश्न

If (x + iy)3 = u + iv, then show that `u/x + v/y  =4(x^2 - y^2)`

योग

उत्तर

`(x  + iy)^3  = u + iv`

or `u  +  iv  = x^3  + 3x^2 .iy  + 3.(iy)^2  x  + (iy)^3`

= `x^3  + 3x^2  yi  + 3xy^2 i^2  + i^3 y^3`   `[∵ i^2 = - 1]`

= `(x^3  - 3xy^2 ) + (3x^2y  -  y^3)i`

⇒ `x^3 - 3xy^2 = u/x`

and `3x^2y  - y^3  = v`

or `3x^2  - y^2 = v/y`

On adding equations, (1) and (2)

`4x^2  - 4y^2  = u/x  +  v/y`

⇒  `u/x + v/y  = 4 (x^2  - y^2)`

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अध्याय 5: Complex Numbers and Quadratic Equations - Miscellaneous Exercise [पृष्ठ ११३]

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एनसीईआरटी Mathematics [English] Class 11
अध्याय 5 Complex Numbers and Quadratic Equations
Miscellaneous Exercise | Q 16 | पृष्ठ ११३

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