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महाराष्ट्र राज्य शिक्षण मंडळएचएससी विज्ञान (सामान्य) इयत्ता ११ वी

The following function has a removable discontinuity? If it has a removable discontinuity, redefine the function so that it become continuous : f(x) =log1+3x(1+5x),for x>0=32x-18x-1, for x<0} at x = 0

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प्रश्न

The following function has a removable discontinuity? If it has a removable discontinuity, redefine the function so that it become continuous :

f(x) `{:(= log_((1 + 3x)) (1 + 5x)",", "for"  x > 0),(=(32^x - 1)/(8^x - 1)",",  "for"  x < 0):}}` at x = 0

बेरीज
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उत्तर

`lim_(x -> 0) "f"(x) =  lim_(x -> 0) log_((1 + 3x)) (1 + 5x)`

= `lim_(x -> 0) [(log (1 + 5x))/(log(1 + 3x))]   ...[because log_"a"x = logx/log"a"]`

= `lim_(x -> 0) ([(log(1 + 5x))/(5x)*5])/([(log (1 + 3x))/(3x)* 3])`    ...[∵ x → 0, ∴ x ≠ 0]

= `5/3 (lim_(x -> 0) [(log(1 + 5x))/(5x)])/(lim_(x -> 0) [(log(1 + 3x))/(3x)])`

= `5/3 xx 1/1    ...[because x -> 0,  therefore 3x -> 0, 5x -> 0  "and" lim_(x -> 0) (log(1 + x))/x = 1]`

= `5/3`     ...(1)

`lim_(x -> 0^-) "f"(x) =  lim_(x -> 0) (32^x - 1)/(8^x - 1)`

= `lim_(x -> 0) (((32^x - 1)/x))/(((8^x - 1)/x))`  ...[∵ x → 0, ∴ x ≠ 0]

= `(lim_(x -> 0) ((32^x - 1)/x))/(lim_(x -> 0) ((8^x - 1)/x))`

= `log32/log8   ...[because lim_(x -> 0) ("a"^x - 1)/x = log "a"]`

= `(log2^5)/(log2^3)`

= `(5log2)/(3log2)`

= `5/3`    ...(2)

From (1) and (2),

`lim_(x -> 0^+) "f"(x) =  lim_(x -> 0^-) "f"(x) = 5/3`

∴ `lim_(x -> 0) "f"(x) = 5/3`

f(0) is not defined

∴ f is discontinuous at x = 0.

This discontinuity is removable.

We redefine the function as follows to make it continuous at x = 0

f(x) `{:(= log_((1 + 3x)) (1 + 5x),","  "for"  x > 0),(= 5/3,","  "for"  x = 0),(=(32^x - 1)/(8^x - 1),","  "for"  x < 0):}`

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  या प्रश्नात किंवा उत्तरात काही त्रुटी आहे का?
पाठ 8: Continuity - EXERCISE 8.1 [पृष्ठ १७४]

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