Question

Is `x=-7` a direct variation and if so what is the constant?

Answer 1

`x=-7` is not a direct variation.

It is not a variation of any kind. `x` is a constant.

A necessary (but not sufficient) condition for an equation to be a direct variation is that the equation have two variables.

Even then the equation would not be a direct variation unless it could be expressed in the form
`color(white)("XXXXX")` `y=c*x` for some constant `c`
(of course the letters `y` and `x` could be replaced by any other two symbols as the variables).