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→Activity No # 2. Angle sum property of a triangle
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# Cut out 3 angles of a triangle and join 3 vertices next to each other.
# Cut out 3 angles of a triangle and join 3 vertices next to each other.
# Repeat for different triangles. What do you infer?
# Repeat for different triangles. What do you infer?
+
+===Activity No # External angle property of a triangle===
+{| style="height:10px; float:right; align:center;"
+|<div style="width:150px;border:none; border-radius:10px;box-shadow: 5px 5px 5px #888888; background:#f5f5f5; vertical-align:top; text-align:center; padding:5px;">
+''[http://www.karnatakaeducation.org.in/?q=node/305 Click to Comment]''</div>
+|}
+* Estimated Time: 40 minutes
+* Materials/ Resources needed: Laptop, geogebra file, projector and a pointer.
+* Prerequisites/Instructions, if any:
+# The students should know a triangle and its basic elements.
+# They should know interior and exterior angles of a triangle.
+# They should know that sum of angles along a straight line is 180 degrees.
+* Multimedia resources: Laptop
+* Website interactives/ links/ Geogebra Applets:
+* Process (How to do the activity):
+# The teacher can move the 'explain slider' to show how the sum of opposite interior angles equals to external angle.
+* Developmental Questions (What discussion questions):
+# Identify the interior angles of this triangle.
+# What are exterior angles ?
+# Name the exterior angle from the figure.
+# Name its two opposite interior angles.
+# What is the measure of the marked exterior angle?
+# What is the sum of two opposite interior angles?
+# What can you infer ?
+* Evaluation :
+# Reason out as to why external angle is equal to sum of opposite interior angles of a triangle.
+* Question Corner:
+# Try to prove external angle theorem using linear pair concept and angle sum property of a triangle
==Concept #2 - Types of triangles==
==Concept #2 - Types of triangles==