Question

define the direct variation

Answer 1

Direct Variation. Directly Proportional. A relationship between two variables in which one is a constant multiple of the other. In particular, when one variable changes the other changes in proportion to the first. If b is directly proportional to a, the equation is of the form b = ka (where k is a constant).

Answer 2

Direct Variation is the variation of one quantity with the multiple of other quantity. 
     Foe eg: if x changes by 2 then y changes by 4.
              y=2x