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Two vectors A and B satisfy the condition that the magnitude of their sum is equal to the magnitude of their difference. What is the angle between A and B?

1. 60°
2. 75°
3. 45°
4. 90°

Correct answer: 90°

Solution

Squaring |A+B|=|A-B| gives 4 A.B = 0, so A.B = 0 and the angle between A and B is 90 deg.

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