Question
Discuss the continuity of the function f, where f is defined by
$\text{f(x)}= \begin{cases}\ 3,\ \ \text{if}\ 0\leq \text{x}\leq 1 \\4,\ \ \text{if}\ 1<\text{x}<3\\5,\ \text{if}\ 3\leq\text{x}\leq10\end{cases}$

Answer

The given function is $\text{f(x)}= \begin{cases}\ 3,\ \ \text{if}\ 0\leq \text{x}\leq 1 \\4,\ \ \text{if}\ 1<\text{x}<3\\5,\ \text{if}\ 3\leq\text{x}\leq10\end{cases}$ The function f is definedc at all points of the interval [0, 10]. Let k be the point in the interval [0, 10]. Then, we have 5 cases i. e. $0\leq\text{k}<1, \text{k}= 1, 1<\text{k}$ $<3, \text{k} = 3\ \text{or}\ 3 < \text{k}\leq 10.$ Now, Case I: $0\leq\text{k}<1$ Then, f(k) = 3 $^{\ \ \text{lim}}_{\text{x}\rightarrow\text{k}}\text{f(x)} = ^{\ \ \text{lim}}_{\text{x}\rightarrow\text{k}}(3) = 3 = \text{f(k)}$ Thus, $^{\ \ \text{lim}}_{\text{x}\rightarrow\text{k}}\text{f(x)} = \text{f(k)}$ Hence, f is continuous in the interval [0, 10]. Case II: k = 1 f(1) = 3 $^{\ \ \text{lim}}_{\text{x}\rightarrow\text{1}^{-}}\text{f(x)} = ^{\ \ \text{lim}}_{\text{x}\rightarrow\text{1}^{-}}(3) = 3$ $^{\ \ \text{lim}}_{\text{x}\rightarrow\text{1}^{+}}\text{f(x)} = ^{\ \ \text{lim}}_{\text{x}\rightarrow\text{1}^{+}}(4) = 4$ $\Rightarrow\ ^{\ \ \text{lim}}_{\text{x}\rightarrow\text{k}^{-}}\text{f(x)} \neq ^{\ \ \text{lim}}_{\text{x}\rightarrow\text{k}^{+}}\text{f(x)}$ Hence, f is not continuous at x = 1. Case III: 1 < k < 3 Then, f(x) = 4 $^{\ \ \text{lim}}_{\text{x}\rightarrow\text{k}}\text{f(x)} = ^{\ \ \text{lim}}_{\text{x}\rightarrow\text{k}}(4) = 4 = \text{f(k)}$ Thus, $^{\ \ \text{lim}}_{\text{x}\rightarrow\text{k}}\text{f(x)} = \text{f(k)}$ Hence, f is continuous in (1, 3). Case IV: k = 3 $^{\ \ \text{lim}}_{\text{x}\rightarrow\text{3}^{-}}\text{f(x)} = ^{\ \ \text{lim}}_{\text{x}\rightarrow\text{3}^{-}}(4) = 4$ $^{\ \ \text{lim}}_{\text{x}\rightarrow\text{3}^{+}}\text{f(x)} = ^{\ \ \text{lim}}_{\text{x}\rightarrow\text{3}^{+}}(5) = 5$ $\Rightarrow\ ^{\ \ \text{lim}}_{\text{x}\rightarrow\text{k}^{-}}\text{f(x)} \neq ^{\ \ \text{lim}}_{\text{x}\rightarrow\text{k}^{+}}\text{f(x)}$ Hence, f is not continuous at x = 3.Case V: $3 < \text{k}\leq 10$
Then, f(k) = 5
$^{\ \ \text{lim}}_{\text{x}\rightarrow\text{k}}\text{f(x)} = ^{\ \ \text{lim}}_{\text{x}\rightarrow\text{k}}(5) = 5 = \text{f(k)}$ Thus $^{\ \ \text{lim}}_{\text{x}\rightarrow\text{k}}\text{f(x)} = \text{f(k)}$ Hence, f is contionuous at all points of the interval [3, 10]. Therefore, x = 1 and 3 are the points of discontinuity of f.

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