Answer:
Direct Variation
Direct variation describes a simple relationship between two variables . We say y varies directly with x (or as x , in some textbooks) if:
y=kx
for some constant k , called the constant of variation or constant of proportionality . (Some textbooks describe direct variation by saying " y varies directly as x ", " y varies proportionally as x ", or " y is directly proportional to x .")
This means that as x increases, y increases and as x decreases, y decreases—and that the ratio between them always stays the same.
The graph of the direct variation equation is a straight line through the origin.
