Give the formula for the area of the following figures: a square, a rectangular, a triangular

• 1.1.1 A square: The formula for the area of a square is the side length squared. $$\text{Area} = \text{side} \times \text{side} = s^2$$
• 1.1.2 A rectangular: The formula for the area of a rectangle is length multiplied by width. $$\text{Area} = \text{length} \times \text{width} = l \times w$$
• 1.1.3 A triangular: The formula for the area of a triangle is half of the base multiplied by the height. $$\text{Area} = \frac{1}{2} \times \text{base} \times \text{height}$$

The side length of the square is $s = 3 \text{ cm}$.

The area of the square ABCD is $\boxed{\text{9 cm}^2}$.

The length of the rectangle is $l = 5 \text{ cm}$ and the width is $w = 3 \text{ cm}$.

The area of the rectangular ABCD is $\boxed{\text{15 cm}^2}$.

First, convert the height from millimeters to centimeters:

The base of the triangle is $\text{AC} = 5 \text{ cm}$ and the height is $\text{DB} = 3 \text{ cm}$.

The area of the triangular ABC is $\boxed{\text{7.5 cm}^2}$.