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The angle between the two vectors A = 3î + 4ĵ + 5k̂ and B = 3î + 4ĵ − 5k̂ will be

1. zero
2. 45°
3. 90°
4. 180°

Correct answer: 90°

Solution

The dot product of A and B is calculated as A·B = (3)(3) + (4)(4) + (5)(-5) = 9 + 16 - 25 = 0. Since the dot product is zero, the angle between the vectors is 90°.

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