Vectors u and v have magnitudes of 20 and 13, respectively, and the angle between them is 210°. What is the scalar projection of u onto v?

The scalar projection of u onto v is |u| cos θ, where θ is the angle between the vectors. Substituting the values gives 20 cos 210° = 20(−√3/2) ≈ −17.32. The correct choice is −17.32.

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