Math Rules for Geometry in 4th Grade

By Jen Kim
Knowing how to calculate the perimeter and area of geometric figures will help you in school and in life.
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For many young students, simply hearing the word "geometry" can send shudders down their spines. But math doesn't have to be that difficult or challenging. The quickest and most effective way to improve math skills begins with a solid foundation in basic geometric principles. Children of all ages should study and practice these major concepts before moving on to more challenging math.


Triangles are one of the most important shapes in elementary geometry. Students will learn how to identify triangle types, based on their sides and angles. For example, a right triangle has one 90-degree angle, an obtuse triangle has an angle that is greater than 90 degrees and an acute triangle is a triangle that has all angles less than 90 degrees. Triangles can also be identified according to their sides: equilateral triangle has three equal sides, an isosceles triangle has two equal sides and a scalene triangle has no equal sides.

Angles and Sides

A polygon is any enclosed shape that has sides, such as a triangle, a square or a trapezoid. For every polygon, the number of sides is equal to the number of angles. For example, a triangle has three sides, so it must have three angles. Practice drawing a variety of polygons, and you will find that the number of sides always equals the number of angles.


In fourth grade geometry, students will begin to learn names for certain shapes called polygons. Regular polygons are those shapes where each side length is equal, such as an equilateral triangle. Most geometry problems and rules will be applied to regular polygons. For example, a square is a regular quadrilateral shape. Polygons are named after their Latin roots: pentagon (5-sided polygon), hexagon (6-sided polygon), heptagon (7-sided polygon), octagon (8-sided polygon), nonagon (9-sided polygon) and decagon (10-sided polygon).

Finding Perimeter and Area

Calculating the perimeter and areas of geometric shapes is a basic concept that math students should master. Perimeter is the total measure of a shape's sides, and area is the total space enclosed by the shape. To calculate the perimeter of a shape, simply add up the sides together. To calculate the area of a regular quadrilateral, multiply the length by the width of a shape. Find the area of a triangle by multiplying the height by the base by ½. For circles, the perimeter is called the circumference, and can be calculated using the formula: c= 2r*pi, where r=radius. The formula for the area of a circle is: A=pi(r^2).


About the Author

Since 2008, Jen Kim has been a professional writer and blogger, working for national publications such as Psychology Today and Chicago Tribune affiliates. She holds a Master of Science in journalism from Northwestern University.