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महाराष्ट्र राज्य शिक्षण मंडळएचएससी विज्ञान (सामान्य) इयत्ता ११ वी

For what values of a and b is the function f(x) =x2-4x-2,for x<2=ax2-bx+3,for 2≤x<3=2x-a+b,for x≥3} continuous for every x on R? - Mathematics and Statistics

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प्रश्न

For what values of a and b is the function

f(x) `{:(= (x^2 - 4)/(x - 2)",", "for"  x < 2),(= "a"x^2 - "b"x + 3",", "for"  2 ≤ x < 3),(= 2x - "a" + "b"",", "for"  x ≥ 3):}}` continuous for every x on R?

बेरीज
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उत्तर

f(x) is continuous for every x on R.

∴ f(x) is continuous at x = 2 and x = 3.

f(x) is continuous at x = 2.

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

∴ `lim_(x -> 2) (x^2 - 4)/(x - 2) =  lim_(x -> 2) ("a"x^2 - "b"x + 3)`

∴ `lim_(x -> 2) ((x - 2)(x + 2))/(x - 2) =  lim_(x -> 2) ("a"x^2 - "b"x + 3)`

∴ `lim_(x -> 2)(x + 2) =  lim_(x -> 2) ("a"x^2 - "b"x + 3)  ...[(because x -> 2  therefore x ≠ 2),(therefore x - 2 ≠ 0)]`

∴ 2 + 2 = a(2)2 – b(2) + 3

∴ 4a – 2b + 3 = 4

∴ 4a – 2b = 1   ...(i)

Also f(x) is continuous at x = 3

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

∴ `lim_(x -> 3)("a"x^2 - "b"x + 3) =  lim_(x -> 3) (2x - "a" + "b")`

∴ a(3)2 – b(3) + 3 = 2(3) – a + b

∴ 9a – 3b + 3 = 6 – a + b

∴ 10a – 4b = 3    ...(ii)

Multiply (i) by 2 and (ii) by 1, we get

8a – 4b = 2    ...(iii)

10a – 4b = 3   ...(iv)

Subtracting (iv) from (iii)

– 2a = – 1

∴ a = `1/2`

Substituting a = `1/2` in (i), we get

`4(1/2) - 2"b"` = 1

∴ 2 – 2b = 1

∴ 1 = 2b

∴ b = `1/2`

∴ a = `1/2` and b = `1/2`

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पाठ 8: Continuity - EXERCISE 8.1 [पृष्ठ १७४]

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