Limits, Continuity and Differentiability Questions and Answers Part-3

1. \[\lim_{x \rightarrow 0}\frac{\sin\left(\pi\cos^{2}x\right)}{x^{2}}\]     equals
a) \[-\pi\]
b) \[\pi\]
c) \[\pi/2\]
d) 1

Answer: b
Explanation:
q21
q21a

2. For \[x \epsilon R ,\lim_{x \rightarrow \infty}\left(\frac{x-3}{x+2}\right)^{x}=\]
a) e
b) \[e^{-1}\]
c) \[e^{-5}\]
d) \[e^{5}\]

Answer: c
Explanation:
q22
q22a

3. The integer n for which \[\lim_{x \rightarrow0}\frac{(\cos x-1)\left(\cos x-e^{x}\right)}{x^{n}}\]      is a finite nonzero number is
a) 1
b) 2
c) 3
d) 4

Answer: c
Explanation:
q23
q23a

4. If f(x) = (x/2) – 1, then on the interval \[\left[0,\pi\right]\]
a) \[\tan (f\left(x\right))\]   and \[\frac{1}{f\left(x\right)}\]   are both continuous
b) \[\tan (f\left(x\right))\]   and \[\frac{1}{f\left(x\right)}\]   are both discontinuous
c) \[\tan (f\left(x\right))\]   and \[f^{-1}\left(x\right)\]   are both continuous
d) neither \[\tan (f\left(x\right))\]   nor \[f^{-1}\left(x\right)\]   is continuous

Answer: c
Explanation: f (x) = (x/2) - 1 is continuous on [0, \[\pi\] ] and
q24

5. The value of \[\lim_{x \rightarrow \beta}\frac{1-\cos\left(ax^{2}+bx+c\right)}{\left(x-\beta\right)^{2}}\]
where \[\alpha,\beta\]  are the distinct roots of \[ax^{2}+bx+c=0\]     is
a) \[\left(\alpha-\beta\right)^{2}\]
b) \[\frac{\left(\alpha-\beta\right)^{2}}{2}\]
c) \[\left(\frac{a\left(\alpha-\beta\right)}{2}\right)^{2}\]
d) none of these

Answer: d
Explanation:
q25

6. \[\lim_{x \rightarrow a}\left\{\left[\left(\frac{a^{1/2}+x^{1/2}}{a^{1/4}-x^{1/4}}\right)^{-1}-\frac{2\left(ax\right)^{1/4}}{x^{3/4}-a^{1/4}x^{1/2}+a^{1/2}x^{1/4}-a^{3/4}}\right]^{-1}-\sqrt{2}^{\log_{4}{a}}\right\}^{8}\]
is
a) a
b) \[a^{3/4}\]
c) \[a^{2}\]
d) none of these

Answer: c
Explanation: Simplifying the expression in brackets by setting a1/4 = b and x1/4 = y, the function whose limit is required can be written as
q26

7. The value of a for which \[\frac{\sin 2x+a\sin x}{x^{3}}\]    tends to a finite limits as \[x\rightarrow 0\]   is
a) 1
b) 2
c) -3
d) none of these

Answer: d
Explanation: Since numerator as well as denominator both
q27

8. If g(x) is a polynomial satisfying g(x) g(y) = g(x) + g(y) + g(xy) -2 for all real x and y and g(2) =5 then \[\lim_{x \rightarrow 3}\] g(x) is
a) 9
b) 25
c) 10
d) none of these

Answer: c
Explanation: Putting x = 2 and y = 1, we have q28
g(x) = xn+1 or g(x)

q28a

9. Let \[f:R\rightarrow R\]   be a function such that \[f\left(\frac{x+y}{2}\right)=\frac{f\left(x\right)+f\left(y\right)}{2}\]     for all x and y , and f(0)= 3 and f'(0) = 3 then
a) \[f\left(x\right)\] /x is continuous on R
b) \[f\left(x\right)\]  is continuous on R
c) \[f\left(x\right)\]  is bounded on R
d) none of these

Answer: b
Explanation:
q29
q29a

10. Given the function f(x) = 1/(1 – x), the number points of discontinuity of the composite function \[y=f^{3n}\left(x\right),\]   where \[f^{n}\left(x\right)=fof\]    .... of (n times ) are \[\left(n\epsilon N\right)\]
a) 0 , 1
b) 2n
c) 3n
d) 2n+1

Answer: a
Explanation: The point x = 1 is a discontinuity of the function
q30