If (-3,4) lies on a curve that is symmetric with respect to the x-axis ,then (3,4) will also lie on the curve.
It is not true.
A graph has symmetry with respect to the x-axis if, whenever (x, y) is on the graph, so is the point (x, -y). In this way, a graph has symmetry with respect to the x-axis if, whenever (3, 4) is on the graph, so is the point (3, -4).