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Let f(x) = ax + b (where a and b are unknown) = x2 + 5 for x ∈ R Find the values of a and b, so that f(x) is continuous at x = 1

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Question

Let f(x) = ax + b (where a and b are unknown)

= x2 + 5 for x ∈ R

Find the values of a and b, so that f(x) is continuous at x = 1

Sum
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Solution

f(x) `{:(= "a"x + "b", x < 1), (= x^2 + 5, x ≥ 1):}`

f(x) = x2 + 5

∴ f(x) = ax + b 

Where, a = 1, b = 5

∴ f(1) = 1 + 5 = 6

L.H.L. = `lim_(x -> 1^-) "f"(x) = lim_(x -> 1^-) ("a"x + "b")` = a + b

R.H.L. = `lim_(x -> 1^+) "f"(x) = lim_(x -> 1^+) (x^2 + 5)` = 1 + 5 = 6

given, f(x) is continuous at n = 1

∴ L.H.L. = R.H.L.

∴ a + b = 6 where, a, b ∈ R

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Chapter 8: Continuity - EXERCISE 8.1 [Page 175]

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