Question 9

Let  $$[x]$$  denote the greatest integer function, and let $$m$$  and  $$n$$  respectively be the numbers of the points  where the function $$f(x) = [x] + |x-2|, -2 < x < 3,$$ is not continuous and not differentiable. Then  $$m+n$$  is equal to:

Consider the function $$f(x) = [x] + |x - 2|$$ for $$-2 < x < 3$$, where $$[x]$$ is the greatest integer function. We need to find $$m + n$$, with $$m$$ denoting the number of points of discontinuity and $$n$$ the number of points of non-differentiability.

Since $$|x - 2|$$ is continuous everywhere and $$[x]$$ is discontinuous at all integers, within the interval $$(-2,3)$$ the integers are $$-1, 0, 1, 2$$. Because $$f(x)$$ combines these two parts and only $$[x]$$ causes discontinuities, it follows that $$f(x)$$ is discontinuous exactly at $$x = -1, 0, 1, 2$$, giving $$m = 4$$.

Next, a function fails to be differentiable either where it is discontinuous or where it has a corner or cusp. From the discontinuities already identified at $$x = -1, 0, 1, 2$$, $$f$$ is non-differentiable at those four points. Although $$|x - 2|$$ introduces a corner at $$x = 2$$, this point has already been counted among the discontinuities. No additional points of non-differentiability arise because between consecutive integers both $$[x]$$ (which is constant) and $$|x - 2|$$ (which is linear) are differentiable. Therefore, $$n = 4$$.

Putting these together yields $$m + n = 4 + 4 = 8$$.

The correct answer is Option (2): 8.

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