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If |z1| = 1(z1 ≠ –1) and z2 = z1-1z1+1, then show that the real part of z2 is zero. - Mathematics

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प्रश्न

If |z1| = 1(z1 ≠ –1) and z2 = `(z_1 - 1)/(z_1 + 1)`, then show that the real part of z2 is zero.

योग
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उत्तर

Let z1 = x + yi

|z1| = `sqrt(x^2 + y^2)` = 1   ......[Given that |z1| = 1]

⇒ x2 + y2 = 1  ......(i)

Now z2 = `(z_1 - 1)/(z_1 + 1)`

= `(x + yi - 1)/(x + yi + 1)`

= `((x + 1) + y"i")/((x + 1) + y"i")`

= `((x - 1) + yi)/((x + 1) + yi) xx (x + 1 - yi)/(x + 1 - yi)`

= `((x - 1)(x + 1) - y(x - 1)i + y(x + 1)i - y^2i^2)/((x + 1)^2 - y^2i^2)`

= `(x^2 - 1 + yi(x + 1 - x + 1) + y^2)/(x^2 + 1 + 2x + y^2)`

= `((x^2 + y^2 - 1) + 2yi)/(x^2 + y^2 + 2x + 1)`

= `((1 - 1))/(x^2 + y^2 + 2x + 1) + (2y)/(x^2 + y^2 + 2x + 1) "i"`

= `0 + (2y)/(x^2 + y^2 + 2x + 1) "i"`

Hence, the real part of z2 is 0.

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अध्याय 5: Complex Numbers and Quadratic Equations - Exercise [पृष्ठ ९२]

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एनसीईआरटी एक्झांप्लर Mathematics [English] Class 11
अध्याय 5 Complex Numbers and Quadratic Equations
Exercise | Q 17 | पृष्ठ ९२

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