Question 12
The function f (x) = (4 − 𝑥^2)/(4𝑥 −𝑥^3 ) is
(A) discontinuous at only one point
(B) discontinuous at exactly two points
(C) discontinuous at exactly three points
(D) none of these
f(x) = (4 − 𝑥^(2 ) )/(4𝑥 − 𝑥^3 )
= (2^2 − 𝑥^(2 ) )/(𝑥(4 − 𝑥^2))
= ((𝟐 − 𝒙)(𝟐 + 𝒙))/(𝒙(𝟐 − 𝒙)(𝟐 + 𝒙))
If we cancel out (2 − 𝑥) and (2 + 𝑥)
Then, we have to assume that x ≠ 2, and x ≠ −2
So, our f(x) becomes
f(x) = 𝟏/𝒙
This function is not defined for x = 0
Thus, f(x) is defined for all points except x = 0, 2, −2
∴ f(x) is discontinuous at exactly 3 points
So, the correct answer is (C)
Made by
Davneet Singh
Davneet Singh is an IIT Kanpur graduate and has been teaching for 16+ years. At Teachoo, he breaks down Maths, Science and Computer Science into simple steps so students understand concepts deeply and score with confidence.
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