Let f : X $\rightarrow$ Y be a function. If every element of co-domain(B) has its pre image in domain(A) under the function f, then the function is said to be onto function.

__Example__:

Is f(x) = 4x -3 onto where f : R $\rightarrow$ R.

**Solution**:

Given that f(x) = 4x -3 where domain is R and co-domain is also R. For

onto function, every element from co-domain has its pre image. So we

will try to solve this y = f(x) = 4x -3 relation for x.

So y = 4x -3

or x = $\frac{y + 3}{4 }$

so every element has its pre image in R(domain).

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