Question

1.) how can we tell if a line on a coordinate plane is a direct variation?
2.) what is the equation that we use to write a proportional relationship?

Explanation:

1. A direct variation line must satisfy two key criteria: it must pass through the origin (0,0) of the coordinate plane, and it must have a constant rate of change (slope) between all points on the line.
2. Proportional relationships are a type of direct variation, and their standard equation uses a constant of proportionality.

Answer:

1. A line is a direct variation if it passes through the origin (0,0) and has a constant slope (rate of change) between all its points.
2. $y = kx$, where $k$ is the non-zero constant of proportionality.