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Find all points of discontinuity of f, where f is defined by f(x)={|x|+3ifx≤-3-2xif-3<x<36x+2ifx≥3 - Mathematics

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प्रश्न

Find all points of discontinuity of f, where f is defined by `f(x) = {(|x|+3, if x<= -3),(-2x, if -3 < x < 3),(6x + 2, if x >= 3):}`

योग

उत्तर

`f(x) = {(|x|+3, if x<= -3),(-2x, if -3 < x < 3),(6x + 2, if x >= 3):}`

For x < -3, f(x) = `abs x + 3:`

-3 < x < 3, f(x) = - 2x and 

x ≥ 3, f(x) = 6x + 2 is a polynomial function.

So this is a function.

⇒ At x = - 3,

`lim_(x -> 3^-) f(x) = lim_(x -> 3^-) (abs x + 3)`

`= lim_(h -> 0) [abs (-3 - h) + 3]`

`= lim_(h -> 0) (6 + h)`

= 6 + 0

= 6

`lim_(x -> 3^+)` f(x) = `lim_(x -> 3^+)` (-2 x)

`= lim_(h -> 0) [-2 (-3 + h)]`

`= lim_(h -> 0) (6 - 2h)`

`= 6 - 2 xx 0`

= 6

Hence, f is continuous at x = -3.

⇒ At x = 3,

`lim_(x -> 3^-)` f(x) = `lim_(x -> 3^-)` (- 2x)

`= lim_(h -> 0) [-2 (3 - h)]`

= `lim_(h -> 0) (- 6 + 2 h)`

`= -6 + 2 xx 0`

= - 6

`lim_(x -> 3^+)` f(x) = `lim_(x -> 3^+)` (6x + 2)

= `lim_(h -> 0)` [6(3 + h) + 2]

 = `lim_(h -> 0)` (18 + 6 h + 2)

 = `lim_(h -> 0)` (20 + 6h)

= 20 + 6 × 0

= 20

Hence, f is not continuous at x = 3

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अध्याय 5: Continuity and Differentiability - Exercise 5.1 [पृष्ठ १५९]

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एनसीईआरटी Mathematics [English] Class 12
अध्याय 5 Continuity and Differentiability
Exercise 5.1 | Q 7 | पृष्ठ १५९

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