Introduce simple, two-dimensional figures. Teach students that polygons are two-dimensional figures with sides and angles. The number of sides and the kinds of angles define the polygon.
Explain that quadrilaterals are polygons with four sides and four angles. Squares have four equal sides and four right angles. Rectangles have two sets of parallel and congruent, or equal, sides and four right angles.
Teach students that triangles are polygons with three sides and three angles. The angles inside a triangle can be acute, obtuse or right angles. Acute angles measure smaller than 90 degrees, obtuse angles measure larger than 90 degrees and right angles measure exactly 90 degrees.
Teach students the difference between perimeter and area. Explain that perimeter measures the distance around an object while area measures the space inside a flat object. Provide examples and reasons for both measurements. For example, a teacher will need to know the perimeter of a bulletin board to find out how much ribbon she needs to create a border around the bulletin board. The teacher will need to know the area of the bulletin board to determine the amount of fabric she needs to cover the inside of the bulletin board.
Teach students to use different formulas to find the perimeter of rectangles, squares and other polygons.
Use the formula P = 2l + 2w, or perimeter equals two times the length plus two times the width, to find the perimeter of a rectangle.
Use the formula P = 4s, or perimeter equals four times the length of one side, to find the perimeter of a square.
To find the perimeter of other polygons, including triangles, add the length of each side.
Teach students to use different formulas to find the area of a rectangle, square and triangle.
Use the formula A = l x w, or area equals length times width, to find the area of a rectangle.
Use the formula A = s x s, or area equals side times side, to find the area of a square.
Finding the area of a triangle takes multiple steps. First, divide the base of the triangle by two and then multiply that number by the height of the triangle. Then divide the product by two. The formula is A = [1/2(b) x h] ÷ 2.