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Electrical mathQuestion 157 of 1506

A vector has the rectangular form −9, −j12. What is its polar form?

  1. 15 @ 53.1°
  2. 15 @ 233.1°
  3. 15 @ 126.9°
  4. 15 @ 306.9°
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Correct answer: 15 @ 233.1°

The magnitude is √(81 + 144) = 15. The calculated angle is arctan(12 ÷ 9) = 53.1°. In quadrant 3 the polar angle is 180° + 53.1° = 233.1°.

Source: Trigonometry and Single Phase AC Generation for Electricians (Flinn), 2.4: Vector Addition

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Questions last reviewed: 18 October 2026