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The non-zero vectors a, b, and c satisfy a=8b and c=-7b. What is the angle between a and c?

1. 0
2. π/4
3. π/2
4. π

Correct answer: π

Solution

The vectors a and c are scalar multiples of the same vector b, with a pointing in the same direction as b and c pointing in the opposite direction. This means that a and c are directly opposite to each other, resulting in an angle of pi (180 degrees) between them.

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