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NCERT Class XI Mathematics - Complex Numbers and Quadratic Equations - Solutions

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Question : 21 of 52
Marks: +1, -0
3\sqrt{3} + i
Solution:  
We have , 3\sqrt{3} + i
Let 3\sqrt{3} = r cosθ …(i) and 1 = r sinθ …(ii)
Squaring and adding (i) and (ii), we get
r2(cos2θ+sin2θ)r^2(\cos^2 \theta + \sin^2 \theta) = 3 + 1 ⇒ r2r^2 = 4 ⇒ r = 2
Substituting the value of r in (i) and (ii), we get 2 cos θ = 3\sqrt{3} , 2 sin θ = 1
⇒ cos θ = 32\frac{\sqrt{3}}{2} , sin θ = 12\frac{1}{2} ⇒ cos θ = cos π6\frac{\pi}{6} , isn θ = sin π6\frac{\pi}{6}
Here , cos θ and sin θ both are positive.
∴ θ lies in first quadrant. ∴ θ = π6\frac{\pi}{6}
∴ The required polar form is z = 2 (cosπ6+isinπ6)\left( \cos \frac{\pi}{6} + i \sin \frac{\pi}{6} \right)
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