How to Identify and Classify Polygons for ACT Math and ACT Subject Test Math Level 1
Polygons are twodimensional shapes that have straight lines as their sides. The sides form a closed loop, which means they do not cross or overlap. The point where two sides meet is called a vertex. Polygons are important topics for both the ACT Math and the ACT subject test Math level 1, as they appear frequently in questions about geometry, algebra, and modeling. In this article, we will explain how to identify and classify polygons based on their number of sides, angles, and other properties.
Types of Polygons Polygons can be classified into different types depending on how many sides they have, how their angles are measured, and whether they are regular or irregular. Here are the main types of polygons you should know:
 Regular Polygons: These are polygons that have all their sides equal in length and all their angles equal in measure. Examples of regular polygons are equilateral triangles, squares, regular pentagons, and regular hexagons.
 Irregular Polygons: These are polygons that do not have all their sides equal in length or all their angles equal in measure. Examples of irregular polygons are scalene triangles, rectangles, trapezoids, and kites.
 Concave Polygons: These are polygons that have at least one angle greater than 180 degrees. This means that some of the vertices point inward, creating a dent or a cave in the shape. Examples of concave polygons are starshaped polygons and arrowheadshaped polygons.
 Convex Polygons: These are polygons that have all their angles less than 180 degrees. This means that none of the vertices point inward, creating a bulge or a convexity in the shape. Examples of convex polygons are triangles, quadrilaterals, pentagons, and hexagons.
 Trigons: These are polygons that have three sides. They are also called triangles. There are different types of triangles based on their side lengths and angle measures, such as equilateral, isosceles, scalene, right, acute, and obtuse triangles.
 Quadrilateral Polygons: These are polygons that have four sides. They are also called quadrilaterals. There are different types of quadrilaterals based on their parallelism and symmetry, such as parallelograms, rectangles, squares, rhombuses, trapezoids, and kites.
 Pentagon Polygons: These are polygons that have five sides. They are also called pentagons. There are different types of pentagons based on their regularity and symmetry, such as regular pentagons, irregular pentagons, concave pentagons, and convex pentagons.
 Hexagon Polygons: These are polygons that have six sides. They are also called hexagons. There are different types of hexagons based on their regularity and symmetry, such as regular hexagons, irregular hexagons, concave hexagons, and convex hexagons.
 Equilateral Polygons: These are polygons that have all their sides equal in length. They can be regular or irregular. Examples of equilateral polygons are equilateral triangles, squares, regular pentagons, and regular hexagons.
 Equiangular Polygons: These are polygons that have all their angles equal in measure. They can be regular or irregular. Examples of equiangular polygons are equilateral triangles, squares, regular pentagons, and regular hexagons.
How to Identify and Classify Polygons on the ACT Math and ACT Subject Test Math Level 1
To identify and classify polygons on the ACT Math and ACT subject test Math level 1, you need to use your knowledge of geometry and algebra to analyze the given shape. You may also need to use a calculator or a protractor to measure the lengths and angles of the sides. Here are some tips to help you identify and classify polygons on these tests:
 Count the number of sides and vertices to determine the basic type of the polygon (trigon, quadrilateral, pentagon, etc.)
 Check if the polygon is regular or irregular by comparing the lengths of the sides and the measures of the angles
 Check if the polygon is concave or convex by looking at the direction of the vertices (inward or outward)
 Check if the polygon is equilateral or equiangular by looking at the equality of the side lengths and angle measures
 Use specific properties and formulas to identify subtypes of polygons (such as parallelograms, rectangles, squares, etc.)
 Use diagrams or sketches to visualize the polygon if it is not given
 Use logic and reasoning to eliminate incorrect choices or find missing information
Examples of Polygon Questions on the ACT Math and ACT Subject Test Math Level 1
Here are some examples of polygon questions that you may encounter on the ACT Math and ACT subject test Math level 1, along with their solutions and explanations:

Example 1: What is the measure of each interior angle of a regular octagon? (ACT Math)
 A) 45 degrees
 B) 60 degrees
 C) 90 degrees
 D) 120 degrees
 E) 135 degrees
 Solution: E) 135 degrees
 Explanation: A regular octagon is a polygon that has eight sides and eight angles that are all equal. To find the measure of each interior angle, we can use the formula for the sum of the interior angles of a polygon, which is (n2)180 degrees, where n is the number of sides. For a regular octagon, n = 8, so the sum of the interior angles is (82)180 = 1080 degrees. To find the measure of each interior angle, we can divide the sum by the number of angles, which is also 8. So, each interior angle is 1080/8 = 135 degrees.

Example 2: In the figure below, ABCD is a parallelogram and E is a point on BC such that BE = EC. What is the measure of angle AED? (ACT Subject Test Math Level 1) ![image]
 A) 30 degrees
 B) 45 degrees
 C) 60 degrees
 D) 75 degrees
 E) 90 degrees
 Solution: C) 60 degrees
 Explanation: A parallelogram is a quadrilateral that has two pairs of parallel sides. One property of a parallelogram is that opposite angles are equal. So, angle A = angle C and angle B = angle D. Since E is the midpoint of BC, we can also say that triangle BEC is an isosceles triangle, which means that its base angles are equal. So, angle BEC = angle BCE. We can use these facts to find the measure of angle AED. First, we can find the measure of angle A by using the fact that the sum of the interior angles of a quadrilateral is 360 degrees. So, angle A + angle B + angle C + angle D = 360. Since angle A = angle C and angle B = angle D, we can simplify this equation to 2(angle A) + 2(angle B) = 360. Dividing both sides by 2, we get angle A + angle B = 180. Now, we can use another property of a parallelogram, which is that consecutive angles are supplementary, meaning they add up to 180 degrees. So, angle A + angle D = 180 and angle B + angle C = 180. Substituting these expressions into the previous equation, we get (angle A + angle D) + (angle B + angle C) = 180. Simplifying, we get 2(angle A) = 180. Dividing both sides by 2, we get angle A = 90 degrees. Since angle A = angle C, we also get angle C = 90 degrees. Next, we can find the measure of angle BEC by using the fact that the sum of the interior angles of a triangle is 180 degrees. So, angle BEC + angle BCE + angle EBC = 180. Since angle BEC = angle BCE and angle EBC = angle C (they are vertical angles), we can simplify this equation to 2(angle BEC) + angle C = 180. Substituting the value of angle C as 90 degrees, we get 2(angle BEC) + 90 = 180. Subtracting 90 from both sides, we get 2(angle BEC) = 90. Dividing both sides by 2, we get angle BEC = 45 degrees. Since angle BEC = angle BCE, we also get angle BCE = 45 degrees. Finally, we can find the measure of angle AED by using the fact that it is an exterior angle of triangle BEC, which means that it is equal to the sum of the opposite interior angles. So, angle AED = angle BEC + angle BCE. Substituting the values of these angles as 45 degrees each, we get angle AED = 45 + 45 = 90 degrees.
I hope this article helped you understand how to identify and classify polygons for ACT Math and ACT subject test Math level 1. If you have any questions or feedback, please let me know in the comments below
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