To Define a Curve's Formula

Open the Curve by Formula dialog ( Drawing > Home > Placement > Create Curves split button).
In the Curve field, key in the curve's name.
Define the equations, finishing each with a semi-colon ;.
(Optional) Place a curve to test the equation.
Save the equation.
Note: Some mathematical knowledge is needed to define a new curve. A curve is defined by the parametric equations for the x, y, and z coordinates of the curve. These formulas give the value of the articular coordinate as a parameter t that is between zero and one (0.0 < t < 1.0). This is the standard parametric form of a curve described in mathematical text books.