How to tell if a function is surjective from its graph

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I am trying to figure out a way to check a function if it is surjective from the graph of the function. I know that we can know about injective functions by drawing a line parallel to x-axis. I am new to this topic and this site as well. Is there any way to check if the range of the function is equal to the codomain?

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2 Answers

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If all line parallel to X-axis ( assuming codomain is whole Y axis) intersect with graph then function is surjective.

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Project the graph onto the $y$-axis and see whether the projection is the whole codomain (=surjective) or a propert part of it (=not surjective)

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