Applications of Derivatives Questions and Answers Part-2

1.The points of contact of the vertical tangents to \[x=2 -3 \sin\theta, y=3+2 \cos\theta\]
are
a) (2, 5), (2, 1)
b) (– 1, 3), (5, 3)
c) (2, 5), (5, 3)
d) (– 1, 3), (2, 1)

Answer: b
Explanation:
q11
q11a

2. If \[f\left(x\right)=\frac{x}{\sin x}\]   and \[g\left(x\right)=\frac{x}{\tan x}\]   where \[0 < x\leq 1\]  , then in this interval
a) both f(x) and g(x) are increasing functions
b) both f(x) and g(x) are decreasing functions
c) f(x) is an increasing function
d) g(x) is an increasing function

Answer: c
Explanation:
q12
q12a

3. The set of all values of a for which the function
\[f\left(x\right)=\left(\frac{\sqrt{a+4}}{1-a}-1\right)x^{5}-3x+\log 5\]
decreases for all real x is
a)\[\left(-3 ,\frac{5-\sqrt{27}}{2}\right)\cup \left(2,\infty\right)\]
b) \[\left(-4 ,\frac{3-\sqrt{21}}{2}\right]\cup \left(1,\infty\right)\]
c) \[\left(-\infty ,\infty\right)\]
d) \[\left[-1 ,\infty\right)\]

Answer: b
Explanation: Differentiating, we get
q13
q13a

4. The function \[g\left(x\right)=e^{ax^{2}}\frac{\log\left(\pi+x\right)}{\log\left(e+x\right)}\left(x\geq 0,a>0\right)\]
is
a) increasing on \[\left[0 ,\infty\right)\]
b) decreasing on \[\left[0 ,\infty\right)\]
c) increasing on \[\left[0,\pi/e\right)\]  and decreasing on \[\left[\pi/e ,\infty\right)\]
d) decreasing on \[\left[0,\pi/e\right)\]  and increasing on \[\left[\pi/e ,\infty\right)\]

Answer: b
Explanation:
q14
q14a

5. The function \[f\left(x\right)=\left(3x^{4}+40x^{3}-0.06x^{2}-1.2x\right)\]
a) decreases on \[\left(-\infty ,0\right)\]
b) increases on \[\left(0 ,\infty\right)\]
c) x = –10 is a point of minimum
d) x = 0.1 is a point of maximum

Answer: c
Explanation:
q15
q15a

6. Let \[f\left(x\right)=xe^{x\left(1-x\right)}\]    , then f (x) is
a) increasing on [– 1/2, 1]
b) decreasing on R
c) increasing on R
d) decreasing on [– 1/2, 1]

Answer: a
Explanation:
q16
q16a

7. The equation \[e^{x-1}+x-2=0\]    as
a) one real root
b) two real root
c) three real root
d) four real root

Answer: a
Explanation: Clearly, x = 1 satisfies the given equation
q17

8. The function f satisfying \[\frac{f\left(b\right)-f\left(a\right)}{b-a}\neq f'\left(x\right)\]
for any \[x\epsilon\] (a, b) is
a) \[f\left(x\right)=x^{1/3},a=-1 , b=1\]
b) \[f\left(x\right)=\begin{cases}2 & x=1\\x^{2}&\ 1< x< 2 ,a=1 , b=2 \\1 &\ x=2 \end{cases}\]
c) \[f\left(x\right)=x \mid x\mid ; a=-1 , b=1\]
d) \[f\left(x\right)=1/x ; a=1 , b=4\]

Answer: b
Explanation: The functions in (a), (c), (d) satisfying hypothesis of Lagrange’s Mean Value theorem so there is
q18

9. Suppose f is differentiable on R and \[a\leq f'\left(x\right) \leq b\]    for all \[x\epsilon R \]  where a, b > 0. If f (0) = 0, then
a) \[f\left(x\right)\leq\min\left(ax ,bx\right)\]
b) \[f\left(x\right)\geq\max\left(ax ,bx\right)\]
c) \[a\leq f\left(x\right)\leq b\]
d) \[ax\leq f\left(x\right)\leq bx\]

Answer: d
Explanation: For x > 0. Applying Lagrange’s theorem on
q19

10. The minimum value of f(x) = |3 – x| + |2 + x| + |5 – x| is
a) 0
b) 7
c) 8
d) 10

Answer: b
Explanation: f can be written as
q20