Question

Is this a linear equation `y^2- 4x=6`?

Answer 1

The answer depends on how you treat `x` and `y`.

If they are both unknowns, then it is not a linear equation, because one of the unknowns (`y`) is raised to a power other than 1.
But on the other hand, if you treat `y` as a constant (like `e` or `pi`) then the only variable (`x`) is raised to the power 1, and the equation becomes linear.