Review the definition of a triangle as a 3-sided polygon.
Explain that today's lesson is about angles in triangles.
Angles in Triangles (15 minutes)
Define the terms "interior angles" and "exterior angles".
Explain that the sum of the interior angles in a triangle is always 180 degrees.
Show examples of triangles and ask students to identify the interior angles.
Have students calculate the missing angles in triangles using the fact that the sum of the interior angles is 180 degrees.
Explain that an exterior angle of a triangle is formed by extending one of the sides of the triangle. The exterior angle is supplementary to the opposite interior angle.
Show examples and have students identify the exterior angles and their corresponding interior angles.
Have students calculate missing angles using exterior angles and the fact that they are supplementary to the opposite interior angle.
Types of Triangles (5 minutes)
Introduce the terms "equilateral", "isosceles", and "scalene" triangles.
Define each type of triangle and show examples.
Challenge Question (5 minutes)
Give students a triangle with missing angles and sides.
Have them identify the type of triangle and calculate the missing angles and sides.
Provide a few different variations of the challenge question so students can work in groups to solve them.
Homework (5 minutes)
Assign students homework to practice calculating missing angles in triangles.
Include a mix of interior and exterior angles.
Have them identify the type of triangle and calculate missing sides as well.
Conclusion
Wrap up the lesson by reviewing what was covered and its importance in mathematics.
Remind students to complete their homework and turn it in on time.