Answer:
the x
Explanation:
Looking at the x in an equation can reveal its shape. A linear graph can look like y=x, y=mx, y=mx+b (m being any number).
When you look at graphs that aren't linear, the x doesn't stand alone in the equation.
Parabolas have a y=x^2 equation. Cubic graphs are y=x^3. They have something attached to the x.
To see all the different kinds of equations and what their graphs look like you can search up "parent functions" and all the basic formulas show up.