Lesson Plan-Grade 8
Lesson Title: Angle
measures
State Standards: MA.8.G.2.3- Demonstrate that the sum of the
angles in a triangle is 180-degrees and apply this fact to find unknown measure
of angles and the sum of angles in polygons
Grade : 8 (FCAT)
Subject: Mathematics
Teaching Aids: Power Point slides
Objectives:
1. Students can prove that the sum of
the angles in a triangle is 1800 by geometrical method.
2. Students will identify
the missing angle in a triangle when other two angles are given.
3. Students can calculate
the sum of the angles of a polygon by dividing into number of triangles.
Lesson Procedure and
Evaluation:
Recapitulation (10 mins):
The student needs to recall the types
of angles , types of triangles and different polygons based on sides.
Explanation: (40 mins)
Activity 1: Help the student prove sum of the angles
in a triangle is 1800.
Use the concepts “alternate angles
are equal” and “ exterior angle = sum of two opposite interior angles” to prove
the above statement
Activity 2: Using the statement “sum of the angles in a triangle is 1800” the
student needs to find missing angle in a given triangle and find all the angles
if it is an Isosceles triangle when only one angle is given
Ex: In
∆ABC, if angle A = 700, angle B = 450, then find
angle c.
Sol: angle c = 1800 – (700
+ 450) = 650.
Activity 3: Finding the sum of angles in a hexagon.
To
find the sum of the angles in a hexagon we divide it into 4 triangles from a
vertex. So 4 x 1800 = 7200 is the sum of interior
angles of a hexagon.
Recapitulation and Evaluation: (10 mins)
- If
in a triangle two angles are 550 and 850 find the
third angle.
- The
unequal angle of an isosceles triangle is 300 Find the other
angles
- Find
the sum of the interior angles of an octagon.
