Question

Which graph represents a proportional relationship?
On a coordinate plane, a straight line with positive slope goes through points (0, 0), (1, 2), and (2, 4).
On a coordinate plane, a vertical line is at x = negative 3.
On a coordinate plane, a horizontal line is at y = 3.
On a coordinate plane, a curved line goes through the origin.

Answer 1

The first graph (the straight line through (0,0), (1,2), (2,4)).

Reason: a proportional relationship is y = kx (a straight line through the origin). The points fit y = 2x (k = 2). The vertical line x = −3, the horizontal line y = 3, and a curved line (even if it passes the origin) are not of the form y = kx.