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If z = x + iy lies in the third quadrant, then z¯z also lies in the third quadrant if ______. - Mathematics

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प्रश्न

If z = x + iy lies in the third quadrant, then `barz/z` also lies in the third quadrant if ______. 

विकल्प

  • x > y > 0

  • x < y < 0

  • y < x < 0

  • y > x > 0

MCQ
रिक्त स्थान भरें

उत्तर

If z = x + iy lies in the third quadrant, then `barz/z` also lies in the third quadrant if x < y < 0

Explanation:

Given that: z = x + iy

If z lies in third quadrant.

So x < 0 and y < 0.

`barz` = x – iy

`barz/z = (x - iy)/(x + iy)`

= `(x - iy)/(x + iy) xx (x - iy)/(x -iy)`

= `(x^2 + i^2y^2 - 2xyi)/(x^2 - i^2y^2)`

= `(x^2 - y^2 - 2xyi)/(x^2 + y^2)`

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

When z lies in third quadrant then `barz/z` will also be lie in third quadrant.

∴ `(x^2 - y^2)/(x^2 + y^2) < 0` and `(-2xy)/(x^2 + y^2) < 0`

⇒ x2 – y2 < 0 and 2xy > 0

⇒ x2 < y2 and xy > 0

So x < y < 0.

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अध्याय 5: Complex Numbers and Quadratic Equations - Exercise [पृष्ठ ९५]

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एनसीईआरटी एक्झांप्लर Mathematics [English] Class 11
अध्याय 5 Complex Numbers and Quadratic Equations
Exercise | Q 37 | पृष्ठ ९५

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