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If |z| = 4 and arg(z) = 5π6, then z = ______. - Mathematics

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Question

If |z| = 4 and arg(z) = `(5pi)/6`, then z = ______.

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Solution

If |z| = 4 and arg(z) = `(5pi)/6`, then z = `underlinebb(-2 sqrt(3) + 2i)`.

Explanation:

Given that:  |z| = 4 and arg(z) = `(5pi)/6`

Let z = x + yi

|z| = `sqrt(x^2 + y^2)` = 4

⇒ x2 + y2 = 16   ......(i)

arg(z) = `tan^-1  (y/x) = (5pi)/6`

⇒ `y/x = tan  (5pi)/6`

= `tan(pi - pi/6)`

= `- tan  pi/6`

= `-1/sqrt(3)`

∴ x = `- sqrt(3) y`  ....(ii)

From equation (i) and (ii),

`(- sqrt(3) y)^2 + y^2` = 16

⇒ 3y2 + y2 = 16

⇒ 4y2 = 16

⇒ y2 = 4

⇒ y = `+-  2`

∴ x = `-2 sqrt(3)`

So, z = `-2 sqrt(3) + 2i`

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Chapter 5: Complex Numbers and Quadratic Equations - Exercise [Page 93]

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NCERT Exemplar Mathematics [English] Class 11
Chapter 5 Complex Numbers and Quadratic Equations
Exercise | Q 25.(x) | Page 93

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