This geometry video tutorial provides a basic introduction into indirect proofs. You need to assume the negation of the conclusion or the statement you're trying to prove. This video contains plenty of examples and practice problems of solving indirect proofs with two column proofs.
Triangle Congruence - SSS, SAS, ASA:
https://www.youtube.com/watch?v=jWHOF6cFbpw
CPCTC - 2 Column Proofs With Triangles:
https://www.youtube.com/watch?v=eq1frp_ZyP8
Hypotenuse Leg Theorem - HL Postulate:
https://www.youtube.com/watch?v=DKSTjS0n3mY
Detour Proofs - Double Triangle Congruence:
https://www.youtube.com/watch?v=1HOrB5yvEl0
The Midpoint Formula:
https://www.youtube.com/watch?v=pzDfd8NXRXk
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Missing Diagrams - 2 Column Proofs:
https://www.youtube.com/watch?v=IaqzuGweGZ8
Right Angle Theorem - SSS & SAS:
https://www.youtube.com/watch?v=FRbFMp8mg1s
Perpendicular Bisector Theorem:
https://www.youtube.com/watch?v=xyNBZuUjmSE
Altitude, Median, Midpoint & P. Bisector:
https://www.youtube.com/watch?v=SyzkgBjXtIs
Parallel & Perpendicular Lines - Slope:
https://www.youtube.com/watch?v=bq3fKZVTflU
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Proving Parallel Lines With Proofs:
https://www.youtube.com/watch?v=0eYzPVgylO8
The Exterior Angle Theorem:
https://www.youtube.com/watch?v=ndqxxAUDF5Y
Exterior Angle Inequality Theorem:
https://www.youtube.com/watch?v=rfMZwrq-wL8
Polygons:
https://www.youtube.com/watch?v=E_-3ulbtcLk
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https://www.video-tutor.net/
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