How to show the angles in a triangle add up to 180 degrees

Part ofShape, space and measures

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A short video on how to show the angles in a triangle add up to 180°.

Triangles up to 180 degrees slideshow

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Click to see a step-by-step slideshow.
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WHAT YOU NEED: piece of card/paper, ruler, scissors and pen.
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STEP 1: Use the ruler to draw a straight horizontal line, draw a diagonal line from the end of the horizontal line...
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...and draw another diagonal line to join the points and mark the angles inside the triangle. Use the scissors to cut the triangle out.
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STEP 2: On another piece of paper, use the ruler to draw another horizontal line.
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STEP 3: Tear each corner off the triangle.
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STEP 4: Place two of the triangles along the horizontal line. Turn the third triangle upside down and slot it between the other two on the line. It should fit perfectly.
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The angles in the triangle you drew all add up to 180°. Remember, all angles on a straight line add up to 180°.

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