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If f(x) = {|x|+ 1x<00x=0|x|-1x>0 For what value (s) of a does limx→a f(x) exists?

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प्रश्न

If f(x) = `{(|x| +  1,x < 0), (0, x = 0),(|x| -1, x > 0):}`

For what value (s) of a does `lim_(x -> a)`  f(x) exists?

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उत्तर

Given function:

f(x)  = `{(|"x"| +  1,"x" < 0), (0, "x" = 0),(|"x"| -1, "x" > 0):}`

(i) at x = 0,

`lim_("x" → 0^-) f("x") = lim_("x"  → 0^-) (1 - "x") = 1`

`lim_("x" → 0^+) f("x") = lim_("x"  → 0^+) ("x" - 1) = -1`

`lim_("x" → 0^-) f("x") ≠ lim_("x" → 0^+) f("x")`

`lim_("x" → 1) f("x")` does not exist at x = 0.

(ii) When a < 0

`lim_("x" → "a"^-) f("x")  = lim_("x" → "a"^-) (1 - "x") = 1 - "a"`

`lim_("x" → "a"^+) f("x")  = lim_("x" → "a"^+) (1 - "x") = 1 - "a"`

∴ `lim_("x" → "a"^-) f("x")  = lim_("x" → "a"^+) f("x")`

That is, `lim_("x" → "a") f("x") = 1 - "a"`

(iii) When a > 0

`lim_("x" → "a"^-) f("x")  = lim_("x" → "a"^-) ("x" - 1) = "a" - 1`

`lim_("x" → "a"^+) f("x")  = lim_("x" → "a"^+) ("x" - 1) = "a" - 1`

∴ `lim_("x" → "a"^-) f("x")  = lim_("x" → "a"^+) f("x")`

Hence, `lim_("x" → "a") f("x") = "a" - 1`

Thus,

When, a < 0, `lim_("x" → "a") f("x") = 1 - "a"`

When, a > 0 `lim_("x" → "a") f("x") = "a" - 1`

Hence, there exists `lim_("x" → "a")` f(x) for all a, a ≠ 0.

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अध्याय 12: Limits and Derivatives - EXERCISE 12.1 [पृष्ठ २३९]

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एनसीईआरटी Mathematics [English] Class 11
अध्याय 12 Limits and Derivatives
EXERCISE 12.1 | Q 30. | पृष्ठ २३९

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