Answer:
Explanation:
I believe you're refering to an "axis of symmetry." This is most often seen in quadratic equations. If the parabolic graph opens up or down, the axis of symmetry is the vertical line passing through the vertex, and the graph is symmetrical about this axis. The same applies to a parabolic graph that opens left or right.
If y = ax^2 + bx + c, the equation of the axis of symmetry is x = -b / (2a).