In day to day life especally in technical related subjects you will find practical use of the Pythagoras theorem. For example a carpenter when a house is being build, who uses the 3,4,5 rules to allign doors and window 90 degees straight up. How does this work? The carpenter prepares three beams with lenghts 3, 4 and 5 meter, or other lengths with the same ratio like 1.5, 2.0 and 2.5 meter. How does he use these beams to align the door or window? He creates a triangle with 1.5m vertical, 2 m horizontal and 2.5 meter sloped. What do you see. The 1.5m length beam is exactly straight up, and can be used to align the door or window to the correct position.