X = -5 can this be expressed as a linear equation in two variables?

True

False

True. You can.

x=-5
x-5 =0
x+0y-5 = 0.
This is the equation in 2 variables, x and y. Here, we have 0y, meaning, value of y is always zero.

You can also use 0z and express it in 3 variables.

But, when you name an equation, you only say the relevant variables.