The catenary curve (also called a chainette, alysoid, funicular, see wiki) - the curve of hanging chain or cable or other fibre in a homogenous gravitational field - is used in many design tasks. To create a sketch shapes as a catenary in Inventor you can zse the function "Equation curve" and specify the curve parametrically.
On the above linked wiki page you can find the generalized equation of a planar catenary curve:

`y = a * cosh (x / a)`

where `a` is the parameter of uniform scaling of the curve.

Start the function Equation curve (*Sketch > Create > Line > Equation curve*):

and enter the equation directly to the equation fieleds - choose the equation option "Explicit" and "Cartesian". Just make sure the correct units are combined - i.e. convert the length value of "x" to angle (mm->rad). Using the value of `a = 1.8` and the range `x` -2 to 2:

`y = 1.8 * cosh (x / 1 mm * 1 rad / 1.8)`