The ordered pair (2, 1) is a solution of a direct variation equation. Write the equation and identify the constant of variation.

A direct variation equation takes the form "b = ka," where the k is the constant of variation. In this case, 1 (b) is one-half as large as 2 (a), so the constant will be 0.5. This would allow the equation to be written as "b = 0.5a," and the constant of variation in this equation is 0.5.