A direct variation is a mathematical relationship between two variables that can be expressed by an equation in which one variable is equal to a constant times the other. In other words, a direct variation is where 
.
In answer a,
, so it is a direct variation.
In answer c,
, so it is a direct variation.
In answer d,
, so it is a direct variation,
Only answer b is left, which means the answer must be 'b'.
We also know 'b' is the answer because it cannot be expressed as <span>. Instead, it is expressed as </span>
, which is not the same thing and is therefore not a direct variation.
Hope I helped, and let me know if you have any questions :)
In answer a,
In answer c,
In answer d,
Only answer b is left, which means the answer must be 'b'.
We also know 'b' is the answer because it cannot be expressed as <span>
Hope I helped, and let me know if you have any questions :)