Consider vectors u and v, where u = ⟨1, –1⟩ and v = ⟨1, 1⟩. What is the measure of the angle between the vectors?

Use the dot product to determine the angle. For u = ⟨1, −1⟩ and v = ⟨1, 1⟩, u · v = (1)(1) + (−1)(1) = 0. Since both vectors are nonzero, a zero dot product means they are perpendicular, so the angle is 90°, choice C.

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