Question 2 - CBSE Class 12 Sample Paper for 2022 Boards (MCQ Based - for Term 1) - Solutions of Sample Papers and Past Year Papers - for Class 12 Boards

Last updated at April 16, 2024 by Teachoo

The value of k (k < 0) for which the function
f
defined as
f (x)={((1 -coskx)/(x sinx ),x≠0 1/2,x=0)┤ is continuous at x = 0 is :

(a) ± 1 (b) −1 (c) ± 1/2 (d) 1/2

This question is
inspired from -
Question 21
- CBSE Class 12 Sample Paper for 2021 Boards

Question 2 The value of k (k < 0) for which the function f defined as π (π₯)={β((1 βcosβ‘ππ₯)/(π₯ sinβ‘π₯ ),π₯β 0@1/2, π₯=0)β€ is continuous at x = 0 is : (a) Β± 1 (b) β1 (c) Β± 1/2 (d) 1/2
Given that function is continuous at x = 0
π(π₯) is continuous at x = 0
i.e. (π₯π’π¦)β¬(π±βπ) π(π)=π(π)
Limit at x β 0
(πππ)β¬(π₯β0) f(x) = (πππ)β¬(ββ0) f(h)
= limβ¬(hβ0) (1 β cosβ‘πβ)/(β (sinβ‘β) )
= limβ¬(hβ0) (π γπ¬π’π§γ^πβ‘γππ/πγ)/(β (sinβ‘β))
= limβ¬(hβ0) (2 sin^2β‘γπβ/2γ)/1 Γ1/(β (sinβ‘β))
= (πππ)β¬(π‘βπ) (π γπππγ^πβ‘γππ/πγ)/(ππ/π)^π Γ (ππ/π)^π/(π (πππβ‘π))
= limβ¬(hβ0) (2 sin^2β‘γπβ/2γ)/(πβ/2)^2 Γ (π^2 β^2)/(4β (sinβ‘β))
= limβ¬(hβ0) sin^2β‘γπβ/2γ/(πβ/2)^2 Γ (π^π π)/(π(πππβ‘π))
= π^π/π limβ¬(hβ0) sin^2β‘γπβ/2γ/(πβ/2)^2 Γ β/sinβ‘β
= π^2/2 limβ¬(hβ0) sin^2β‘γπβ/2γ/(πβ/2)^2 Γlimβ¬(hβ0) β/sinβ‘β
= π^2/2 Γ 1 Γ 1
= π^π/π
Now,
(π₯π’π¦)β¬(π±βπ) π(π)=π(π)
π^2/2 = 1/2
π^2 =1
π =Β±π
But, given that k < 0
Thus, only value is k = β1
So, the correct answer is (b)

Made by

Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science and Computer Science at Teachoo

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