Let f be defined on D=ℝ-{-1,1} by fx=|x|1-|x|, then

(C) f is continuous but not differentiable on D

(D) f is differentiable but not continuous on D

AP EAMCET · Maths · Continuity and Differentiability

Let $f$ be defined on $D = ℝ - {- 1, 1}$ by $f (x) = \frac{| x |}{1 - | x |}$ , then

A $f$ is differentiable on $D$
B $f$ is differentiable on $D$ except at $x = 0$
C $f$ is continuous but not differentiable on $D$
D $f$ is differentiable but not continuous on $D$

Verified Solution

Answer & Solution

Correct Answer

(B) $f$ is differentiable on $D$ except at $x = 0$

Step-by-step Solution

Detailed explanation

Given: f(x)=|x|1-|x| Now, LHL=limx→0-fx =limh→0f0-h =limh→00-h1-0-h=0 RHL=limx→0+fx =limh→0f0+h =limh→00+h1-0+h=0 limx→0-fx=limx→0+fx=f0 Hence, fx is continuous at x=0. Using differentiation:…

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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