If the equation of a demand curve takes the form pq = e, where e is constant. If expenditure is always same and equals to e, then the demand curve will be in the shape of.

Rectangular Hyperbola

The given demand curve, pq=e, represents a rectangular hyperbola.

Explanation:

The equation pq=e can be rearranged to $or\; q=e/p$, which is the standard form of a hyperbolic curve. This equation implies an inverse relationship between price ($p$) and quantity demanded (q), which is a characteristic of a hyperbolic curve.