You walk from your home to school, you walk back from your school to home. Outcome: you have walked two lots of the distance between your home and school but your resulting displacement is 0: you are now exactly where you started from. The sum of two vectors of the same magnitude but in opposite directions is 0.
Another example: try rowing a boat across a flowing stream. To go to the opposite bank you need to aim up-stream. Alternatively, if you try to row at right angles to the bank that you started from, you will end up downstream. These are examples of adding vectors that are acting at an angle to one another.
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