Obtain a printed copy of a large scalene triangle, or draw one on a sheet of paper. Cut the triangle out, and tear off each of the three corners. Move the corners so that they form a line, as such:

“What is the angle measure of a line, or straight angle? If all 3 angles from the triangle formed the line, then what can you say about the angles?”

Watch this video if necessary:

Triangle Sum Theorem Proof

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