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If f(x) =sin2x5x-a,for x>0=4,for x=0=x2+b-3,for x<0} is continuous at x = 0, find a and b - Mathematics and Statistics

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Question

If f(x) `{:(= (sin2x)/(5x) - "a"",", "for"  x > 0),(= 4 ",", "for"  x = 0),(= x^2 + "b" - 3",", "for"  x < 0):}}` is continuous at x = 0, find a and b

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Solution

f(x) is continuous at x = 0

∴ `lim_(x -> 0^+) "f"(x)` = f(0)

∴ `lim_(x -> 0^+) ((sin2x)/(5x) - "a")` = 4

∴ `lim_(x -> 0^+) (sin 2x)/(5x) - lim_(x -> 0^+) "a"` = 4

∴ `1/5 lim_(x -> 0^+) (sin2x)/(2x) xx (2) - lim_(x -> 0^+) "a"` = 4

∴ `1/5 (1) (2) - "a"` = 4     ...`[(because  x -> 0","  2x -> 0),(lim_(x -> 0^+) sintheta/theta = 1)]`

∴ `2/5 - "a"` = 4

∴ `2/5 - 4` = a

∴ a = `-18/5`

Also, `lim_(x -> 0^+) "f"(x)` = f(0)

∴ `lim_(x -> 0^+) (x^2 + "b" - 3)` = 4

∴ b – 3 = 4

∴ b = 7

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Chapter 8: Continuity - EXERCISE 8.1 [Page 174]

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