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Question

The modulus- amplitude form of \(\sqrt 3 + i\) , where \(i = \sqrt { - 1}\)  is

This question was previously asked in
NDA I 2018 GAT Previous Year Paper (22-Apr-2018)
The correct answer is \(2\left( {\cos \frac{\pi }{6} + i\sin \frac{\pi }{6}} \right)\)

Understanding Modulus-Amplitude Form of Complex Numbers

The modulus-amplitude form, also known as the polar form, represents a complex number \(z = x + iy\) in terms of its distance from the origin (modulus, \(r\)) and the angle it makes with the positive x-axis (amplitude or argument, \(\theta\)). The general form is given by \(z = r(\cos \theta + i \sin \theta)\).

Finding Modulus and Amplitude for \(\sqrt 3 + i\)

We are given the complex number \(z = \sqrt 3 + i\). This is in the Cartesian form \(x + iy\), where \(x = \sqrt 3\) and \(y = 1\).

Calculating the Modulus

The modulus \(r\) of a complex number \(z = x + iy\) is calculated using the formula \(r = \sqrt{x^2 + y^2}\). For \(z = \sqrt 3 + i\): \(r = \sqrt{(\sqrt 3)^2 + (1)^2}\) \(r = \sqrt{3 + 1}\) \(r = \sqrt{4}\) \(r = 2\) So, the modulus of \(\sqrt 3 + i\) is 2.

Finding the Argument (Amplitude)

The argument \(\theta\) is the angle such that \(\cos \theta = \frac{x}{r}\) and \(\sin \theta = \frac{y}{r}\). Using the values \(x = \sqrt 3\), \(y = 1\), and \(r = 2\): \(\cos \theta = \frac{\sqrt 3}{2}\) \(\sin \theta = \frac{1}{2}\) Since both \(\cos \theta\) and \(\sin \theta\) are positive, the angle \(\theta\) lies in the first quadrant. The angle whose cosine is \(\frac{\sqrt 3}{2}\) and sine is \(\frac{1}{2}\) is \(\frac{\pi}{6}\) radians (or 30 degrees). Therefore, the argument \(\theta = \frac{\pi}{6}\).

Writing the Modulus-Amplitude Form

Now, substituting the values of \(r\) and \(\theta\) into the modulus-amplitude form \(z = r(\cos \theta + i \sin \theta)\): \(z = 2\left(\cos \frac{\pi}{6} + i \sin \frac{\pi}{6}\right)\) This is the modulus-amplitude form of the complex number \(\sqrt 3 + i\).

Comparing with Options

Let's compare our result \(2\left(\cos \frac{\pi}{6} + i \sin \frac{\pi}{6}\right)\) with the given options to find the correct representation. The calculated form matches one of the provided options.
Component Value
Complex Number \(z\) \(\sqrt 3 + i\)
Real Part \(x\) \(\sqrt 3\)
Imaginary Part \(y\) \(1\)
Modulus \(r\) \(2\)
Argument \(\theta\) \(\frac{\pi}{6}\)
Modulus-Amplitude Form \(2\left(\cos \frac{\pi}{6} + i \sin \frac{\pi}{6}\right)\)

The modulus-amplitude form is \(2\left(\cos \frac{\pi}{6} + i \sin \frac{\pi}{6}\right)\).
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Important Questions from Complex Numbers

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