x2/a2+y2/b2=1
If you mean
x^2 / a^2 + y^2 / b^2 = 1
This is the graph of an ellipse ..... (assuming a ≠ b)...... centered at the origin......with its vertices located at (±a, 0) and (0, ±b)
If a = b, we just have a circle centered at the origin with a = b = r
the meaning is not clear.
x^2 = x2
or
x_2 = x2