An angle measuring (870n)° is in standard position. For which value of n will the terminal side fall on the y-axis?

A terminal side lies on the y-axis when the angle is an odd multiple of 90°, or equivalently when it is congruent to 90° modulo 180°. For n = 3, the angle is 870 × 3 = 2610°, and 2610° = 7 × 360° + 90°. So its terminal side lies on the positive y-axis; the correct choice is A, n = 3.

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