Answer:
The direct variation says that:
Then the equation is of the form:
where k is the constant of Variation.
As per the statement:
A number b varies directly with the number a.
i.e
By definition of direct variation:
.....[1]
if and
Substitute in [1] we get k;
Divide both sides by we get;
1 = -k
or
k = -1
⇒equation becomes: b = -a
Therefore, an equation represents this direct variation between a and b is: