Course Guide - USAID Teacher Education Project

This is where the activity, ripping the corners off a triangle and rearranging them toform a straight angle, can illustrate that while a straight angle does not have a corner,it indeed has a vertex, which is where the three angles ripped from the triangle cometogether.h) Interior angle sums of triangles: A discussion of straight angles by older childrenis an appropriate lead-in to determining the angle sum of a triangle.Children may be comfortable knowing that triangles, even those that look differentfrom each other, all have: 1) three sides and 2) three angles.But there is a third attribute of all triangles: the sum of the angles in any triangleequals 180°. Telling children this fact is not enough. They need to experiment with avariety of triangles to prove that the three angles of any triangle will form a straightangle of 180°.This fact will become important as older children realize that they can subdivide anypolygon into triangles and calculate the polygon’s angle sum.3. What is essential to know or do in class?a) Introduce the three models for angles: wedge, branch, and dynamic/rotational.b) Assess if students understand that the size of an angle is determined by itsmeasurement in degrees, not the length of its two line segments.c) Angles can be categorized by measurement: while students may be able to describeacute, right, and obtuse angles, they may not be familiar with the idea of straight,reflex, and whole angles.d) Have students conjecture about the sum of the interior angles of a triangle, thenhave them prove or disprove their initial ideas in order to reach the generalization thatall triangles have an angle sum of 180°, not just special cases such as equilateral (60°-60°-60°) or isosceles right (90°-45°-45°) triangles.4. Class Activitiesa) Types of angles: Have students recall what they said when describing angles inSession 1's pre-assessment.Most likely they will refer to types of angles characterized by measurement indegrees. By drawing pictures similar to the ones above, introduce the idea of wedgeangles within a closed figure (such as the triangle and bread slices) and angles thatradiate out from a vertex like branches of a tree.Use the analog clock to ask about angles formed when the minute hand moves aroundthe clock's center. Ask how they would determine the time if the clock face did nothave numbers.