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IS Y=X^3 IS ONTO WHERE X AND Y BELONGS TO SET OF INTEGERS???

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No, as for a function to be ONTO for every element y in the co-domain there exist some x in the domain  such that

F(X)=Y

Now for X=Y3

as X and Y belong to integer every image in the co-domain doesn't have preimage  in the domain

for example, let Y=3

Now there is no integer whose cube is 3.

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