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महाराष्ट्र राज्य शिक्षण मंडळएचएससी विज्ञान (सामान्य) इयत्ता ११ वी

Test the continuity of the following function at the point or interval indicated against them : f(x) =(27-2x)13-39-3(243+5x)15, for x≠0=2, for x=0} at x = 0.

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प्रश्न

Test the continuity of the following function at the point or interval indicated against them :

f(x) `{:(= ((27 - 2x)^(1/3) - 3)/(9 - 3(243 + 5x)^(1/5))",",  "for"  x ≠ 0),(= 2",",  "for"  x = 0):}}` at x = 0.

बेरीज
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उत्तर

f(0) = 2     ...(Given)

`lim_(x -> 0) "f"(x) =  lim_(x -> 0) ((27 - 2x)^(1/3) - 3)/(9 - 3(243 + 5x)^(1/5))`

= `lim_(x -> 0) ((27 - 2x)^(1/3) - 3)/(-3[(243 + 5x)^(1/5) - 3]`

= `(-1)/(3)  lim_(x -> 0) ((27 - 2x)^(1/3) - (27)^(1/3))/((243 + 5x)^(1/5) - (243)^(1/5))`

= `(-1)/(3) lim_(x -> 0)  (((27 - 2x)^(1/3) - 27^(1/3))/((27 - 2x) - 27) xx [(27 - 2x) - 27])/(((243 + 5x)^(1/5) - (243)^(1/5))/((243 + 5x) - 243) xx [(243 + 5x) - 243])`

...`[("As"  x -> 0"," -2x -> 0 and 5x -> 0),(therefore (27 - 2x) - 27 -> 0 and (243 + 5x) - 243 -> 0),(therefore (27 - 2x) - 27 ≠ 0 and (243 + 5x) - 243 ≠ 0)]`

= `(-1)/(3) (lim_(x -> 0) ((27 - 2x)^(1/3) - 27^(1/3))/((27 - 2x) - 27) xx (-2x))/(lim_(x -> 0) ((243 + 5x)^(1/3) - (243)^(1/5))/((243 + 5x) - 243) xx (5x)`

= `(-1)/(3) xx (-2)/(5) xx (lim_(x -> 0)((27 - 2x)^(1/3) - 27^(1/3))/((27 - 2x) - 27))/(lim_(x -> 0) ((243 + 5x)^(1/5) - (243)^(1/5))/((243 + 5x) - 243)`  ...[∵  x  → 0, x ≠ 0]

= `2/15 xx (1/3(27)^((-2)/3))/(1/5(243)^((-4)/5))  ...[because  lim_(x -> "a") (x^"n" - "a"^"n")/(x - "a") = "na"^("n" - 1)]`

= `2/15 xx 5/3 xx ((3^3)^((-2)/3))/((3^5)^((-4)/5))`

= `2/9 xx (3)^(-2)/(3)^(-4)`

= `2/9 xx (3)^2`

= 2

∴ `lim_(x -> 0) "f"(x)` = f(0)

∴ f(x) is continuous at x = 0

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पाठ 8: Continuity - EXERCISE 8.1 [पृष्ठ १७३]

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