What is the formula to calculate the area of a rectangle?

The formula for calculating the area of a rectangle is determined by multiplying its length by its width. This formula arises from the geometric definition of area, which is the amount of space enclosed within a shape. In the case of a rectangle, you can visualize this by considering a rectangle composed of unit squares; the total number of squares that fit within the length and width gives you the area.

To clarify further, this calculation results from determining how many units fit along the rectangle's length and width. For example, if a rectangle has a length of 5 units and a width of 3 units, the area would be calculated as 5 x 3, yielding an area of 15 square units.

The other options represent different shapes or calculations: one indicates addition rather than multiplication, another relates to the area of a triangle, and the last one is the formula for the area of a circle. Each of these formulas serves a specific shape and context, demonstrating that understanding the correct formulas for different geometric shapes is crucial in mathematics.