A line that divides a figure into two equal parts

The answer is: Only one straight.

A straight line divides a figure into two exactly symmetrical parts, of equal shape and area. The answer to the question of how many straight lines divide a figure into two equal parts depends on the specific properties of the geometry. For example, a triangle can be divided into two equal parts by one straight line, while a quadrilateral requires two lines. In either case, the line or lines divide the figure into two exactly equal parts.