If `A={1,\ 2,\ 3}` , show that an onto function `f: A->A` must be one-one

Explanation

We have given,` f:A->A`
As `A={1,2,3}`

∴ Function `f:{1,2,3}->{1,2,3}`

(i) `f(1)=1,f(2)=2,f(3)=3`

(ii)` f(1)=1,f(2)=3,f(3)=2`

(iii) `f(1)=2,f(2)=3,f(3)=1`

(iv) `f(1)=2,f(2)=1,f(3)=3`

(v)` f(1)=3,f(2)=1,f(3)=2`

(vi)` f(1)=3,f(2)=2,f(3)=1`

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