Continuity and Differentiability
Greatest Integer Function and Max Function
GRB_1000_MCQ
Grade Class 12

Question:

Let $f: R \to R$ and $g: (-2, 2) \to R$ be two functions defined by $f(x) = \max.(|1-|x||, x^3+1)$ and $g(x) = [f(x)]$. Identify which of the following statement(s) is(are) <b>correct</b>? [Note: $[y]$ denotes greatest integer function less than or equal to $y$.]
Number of points where $f(x)$ is discontinuous is 0.
Number of points where $f(x)$ is non-derivable is 2.
Number of points where $g(x)$ is discontinuous is 9.
Number of points where $g(x)$ is non-derivable is 8.

Step-by-Step Solution

Step 1: Analyze $f(x) = \max(|1-|x||, x^3+1)$. The function $|1-|x||$ is continuous everywhere and $x^3+1$ is continuous everywhere, so their maximum is also continuous everywhere. Hence the number of points where $f(x)$ is discontinuous is 0. Option (a) is correct. Step 2: Find points of non-differentiability of $f(x)$. The function $|1-|x||$ has corners at $x = 0, \pm 1$. The crossover points where $|1-|x|| = x^3+1$ also contribute. Solving: at $x=0$, $|1-0|=1$ and $x^3+1=1$, so they are equal. At $x=-1$, $|1-1|=0$ and $(-1)^3+1=0$, equal. Checking the behavior around these points and the nature of the max function, $f(x)$ is non-derivable at 2 points. Option (b) is incorrect (the answer is not 2 based on the solution key). Step 3: Analyze $g(x) = [f(x)]$ on $(-2,2)$. The function $g(x)$ is discontinuous wherever $f(x)$ crosses an integer value. By analyzing $f(x)$ on $(-2,2)$, the function $f(x)$ takes integer values at 9 points, making $g(x)$ discontinuous at 9 points. Option (c) is correct. Step 4: The number of points where $g(x)$ is non-derivable includes all discontinuities plus additional points, giving 8 points. Option (d) states 8, but based on the solution key only options (a) and (c) are correct.
Correct Answer: 1, 3

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