It is possible to draw more than two different rectangles with an area of 36 square units because there is more than one pair of whole numbers that multiply to 36. A 36 square unit rectangle could be made by 1x36, 2x18, 3,12, 4x9, or 6x6.
A 15 square unit triangle, however, can only be made with 1x15 and 3x5 because those are the only whole numbers that divide evenly into 15.