Question
Let $a_1, a_2, ..., a_n$ be fixed real numbers such that $f(x) = (x - a_1)(x - a_2) ...(x - a_n)$ What is $\lim\limits_{\text{x}\rightarrow\text{a}_1}\text{f(x)}?$ For $\text{a}\ne\text{a}_1,\text{a}_2,\dots\text{a}_\text{n}$ compute $\lim\limits_{\text{x}\rightarrow{\text{a}}}\text{f(x)}.$

Answer

$\lim\limits_{\text{x}\rightarrow{\text{a}}}\text{f(x)}$
$\Rightarrow\lim\limits_{\text{x}\rightarrow\text{a}_1}({\text{x}-{\text{a}_1}})(\text{x}-\text{a}_2)\dots(\text{x}-\text{a}_\text{n})$ [Putting limits $x \rightarrow a_1$]
$\Rightarrow(\text{a}_1-\text{a}_1)(\text{a}_1-\text{a}_2)\dots(\text{a}_1-\text{a}_\text{n})$
$\Rightarrow0$
And,
$\lim\limits_{\text{x}\rightarrow{\text{a}}}\text{f(x)}$
$\Rightarrow\lim\limits_{\text{x}\rightarrow{\text{a}}}(\text{x}-\text{a}_1)(\text{x}-\text{a}_2)\dots(\text{x}-\text{a}_\text{n})$ [Putting limit $x \rightarrow a$]
$\Rightarrow(\text{a}-\text{a}_1)(\text{a}-\text{a}_2)\dots(\text{a}-\text{a}_\text{n}).$

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