MHT CET · Maths · Continuity and Differentiability

Let
\(f(x) \begin{cases}=|x|+3, & \text { if } x \leq-3 \ =-2 x, & \text { if }-3 < x < 3, \end{cases}\) \(\text { then } \ =6 x+2, \text { if } x \geq 3\)

A \(f(x)\) is discontinuous at both \(x=-3\) as well as \(x=3\)
B \(f(x)\) is continuous at \(x=-3\) but discontinuous at \(x=3\)
C \(f(x)\) is continuous at \(x=-3\) as well as \(x=3\)
D \(f(x)\) of discontinuous at \(x-3\) but \(f(x)\) is continuous at \(x=3\)

Verified Solution

Answer & Solution

Correct Answer

(B) \(f(x)\) is continuous at \(x=-3\) but discontinuous at \(x=3\)

Step-by-step Solution

Detailed explanation

We have \(f(x)=-x+3\), if \(x \leq-3\)
\(=-2 x \text {, if }-3 < x < 3 \)
\( =6 \mathrm{x}+2 \text {, if } \mathrm{x} \geq 3 \)
\( \underset{x \rightarrow 3^{-}}{f(x)}=-(-3)+3=6 \text { and } \underset{x \rightarrow 3^{+}}{f(x)}=-2(-3)=6\) \(\text { and } f(-3) \)
\( =-(-3)+3=6\)
Thus \(\mathrm{f}(\mathrm{x})\) is continuous at \(\mathrm{x}=-3\)
\(
\underset{x \rightarrow 3^{-}}{f(x)}=-2(3)=-6 \quad \text { and } \underset{x \rightarrow 3^{+}}{f(x)}=6(3)+2=20
\)
Thus \(\mathrm{f}(\mathrm{x})\) is not continuous at \(\mathrm{x}=3\).

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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Let\(f(x) \begin{cases}=|x|+3, & \text { if } x \leq-3 \ =-2 x, & \text { if }-3 < x < 3, \end{cases}\) \(\text { then } \ =6 x+2, \text { if } x \geq 3\)

Step-by-step Solution

Let
\(f(x) \begin{cases}=|x|+3, & \text { if } x \leq-3 \ =-2 x, & \text { if }-3 < x < 3, \end{cases}\) \(\text { then } \ =6 x+2, \text { if } x \geq 3\)