What is the polar form of negative 9 square root of 3 plus 9 i ?

For the complex number −9√3 + 9i, the modulus is √((−9√3)² + 9²) = √(243 + 81) = 18. Its real part is negative and its imaginary part is positive, so it lies in Quadrant II; the reference angle is 30° because tan(θ) = 9/(9√3) = 1/√3. Thus its angle is 150°, giving 18(cos 150° + i sin 150°), choice A.

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