MCQ
The function $f : R \rightarrow R$ defined by $f(x) = (x - 1)(x - 2)(x - 3)$ is:
  • A
    One$-$one but not onto.
  • Onto but not one$-$one.
  • C
    Both one and onto.
  • D
    Neither one$-$one nor onto.

Answer

Correct option: B.
Onto but not one$-$one.
Given function is $f(x) = (x - 1)(x - 2)(x - 3)$
If $f(x) = f(y)$ then
$(x - 1)(x - 2)(x - 3) = (y - 1)(y - 2)(y - 3)$
$\Rightarrow f(1) = f(2) = f(3) = 0$
It is not one$-$one.
$y = f(x)$
$\text{x}\in\text{R}$ also $\text{y}\in\text{R}$ hence $f$ is onto.

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