User:Georgejem/Origami in Mathematics Pedagogy/Lesson Plans for Upper Primary Classes/Sum Property of Triangles

MODEL: ORIGAMI DOLPHIN

crease pattern of origami dolphin

STEP 1: SQUARE SHEET OF PAPER Ask students to describe the shape. (E.g., the square has 4 sides. They are of equal length.) Observe that all angles in the square are 90⁰. They are all right angles.

STEP 2: FOLD ALONG ONE DIAGONAL The square is now two triangles. They are right-angled triangles (By observation above.) Measure the other two angles using protractor. They are 45⁰. Add up all the interior angles of one triangle. They add up to 180⁰. This is the sum property of triangles.

STEP 3: FOLD SIDES TO THE DIAGONAL LINE Now there are four triangles. Are they all right-angled triangles? Measure their interior angles of each triangle. What do they add up to?

STEP 4: FOLD OTHER TWO SIDES TO THE DIAGONAL LINE Are there more right triangles formed? What are the angles of the triangles formed? Are they the same as the ones in the previous step?

STEP 5: FOLD ALONG THE OTHER DIAGONAL How many triangles are there in the paper now? How many are right-angled triangles?