Which coordinate pair identifies a point on the plane?

• A. (x, y)
• B. (y, x)
• C. [x, y]
• D. {x, y}

Answer: (A)

On a 2D plane, a location is named by an ordered pair written with parentheses: (x, y). The first number tells how far to the right (positive) or left (negative) from the origin, and the second tells how far up (positive) or down (negative). This format uniquely identifies a point.

Other forms aren’t used to name a point in the plane. [x, y] is typically a list or vector, and {x, y} is a set, which loses the important order. (y, x) would swap the coordinates, placing you at a different point. So the standard, unambiguous way to name a point is (x, y). For example, (3, 4) means 3 units right and 4 units up from the origin.