JEE MAIN - Mathematics (2019 - 9th April Morning Slot)

1
If the standard deviation of the numbers –1, 0, 1, k is $$\sqrt 5$$ where k > 0, then k is equal to
Answer
(A)
2$$\sqrt 6 $$
2
Let p, q $$ \in $$ R. If 2 - $$\sqrt 3$$ is a root of the quadratic equation, x2 + px + q = 0, then :
Answer
(A)
p2 – 4q – 12 = 0
3
Let ƒ(x) = 15 – |x – 10|; x $$ \in $$ R. Then the set of all values of x, at which the function, g(x) = ƒ(ƒ(x)) is not differentiable, is :
Answer
(D)
{5,10,15}
4
If ƒ(x) is a non-zero polynomial of degree four, having local extreme points at x = –1, 0, 1; then the set
S = {x $$ \in $$ R : ƒ(x) = ƒ(0)}
Contains exactly :
Answer
(C)
two irrational and one rational number.
5
The value of $$\int\limits_0^{\pi /2} {{{{{\sin }^3}x} \over {\sin x + \cos x}}dx} $$ is
Answer
(D)
$${{\pi - 1} \over 4}$$
6
Let $$\overrightarrow \alpha = 3\widehat i + \widehat j$$ and $$\overrightarrow \beta = 2\widehat i - \widehat j + 3 \widehat k$$ . If $$\overrightarrow \beta = {\overrightarrow \beta _1} - \overrightarrow {{\beta _2}} $$, where $${\overrightarrow \beta _1}$$ is parallel to $$\overrightarrow \alpha $$ and $$\overrightarrow {{\beta _2}} $$ is perpendicular to $$\overrightarrow \alpha $$ , then $${\overrightarrow \beta _1} \times \overrightarrow {{\beta _2}} $$ is equal to
Answer
(B)
$${1 \over 2}$$($$ - 3\widehat i + 9\widehat j + 5\widehat k$$)
7
All the points in the set
$$S = \left\{ {{{\alpha + i} \over {\alpha - i}}:\alpha \in R} \right\}(i = \sqrt { - 1} )$$ lie on a :
Answer
(C)
circle whose radius is 1.
8
If $$\left[ {\matrix{ 1 & 1 \cr 0 & 1 \cr } } \right]\left[ {\matrix{ 1 & 2 \cr 0 & 1 \cr } } \right]$$$$\left[ {\matrix{ 1 & 3 \cr 0 & 1 \cr } } \right]$$....$$\left[ {\matrix{ 1 & {n - 1} \cr 0 & 1 \cr } } \right] = \left[ {\matrix{ 1 & {78} \cr 0 & 1 \cr } } \right]$$,

then the inverse of $$\left[ {\matrix{ 1 & n \cr 0 & 1 \cr } } \right]$$ is
Answer
(C)
$$\left[ {\matrix{ 1 & { - 13} \cr 0 & 1 \cr } } \right]$$
9
If the function ƒ : R – {1, –1} $$ \to $$ A defined by
ƒ(x) = $${{{x^2}} \over {1 - {x^2}}}$$ , is surjective, then A is equal to
Answer
(C)
R – [–1, 0)
10
If one end of a focal chord of the parabola, y2 = 16x is at (1, 4), then the length of this focal chord is :
Answer
(C)
25
11
If the function ƒ defined on , $$\left( {{\pi \over 6},{\pi \over 3}} \right)$$ by $$$f(x) = \left\{ {\matrix{ {{{\sqrt 2 {\mathop{\rm cosx}\nolimits} - 1} \over {\cot x - 1}},} & {x \ne {\pi \over 4}} \cr {k,} & {x = {\pi \over 4}} \cr } } \right.$$$ is continuous, then k is equal to
Answer
(C)
$${1 \over 2}$$
12
The value of cos210° – cos10°cos50° + cos250° is
Answer
(B)
$${3 \over 4}$$
13
Let $$\sum\limits_{k = 1}^{10} {f(a + k) = 16\left( {{2^{10}} - 1} \right)} $$ where the function ƒ satisfies
ƒ(x + y) = ƒ(x)ƒ(y) for all natural numbers x, y and ƒ(1) = 2. then the natural number 'a' is
Answer
(D)
3
14
Four persons can hit a target correctly with probabilities $${1 \over 2}$$, $${1 \over 3}$$, $${1 \over 4}$$ and $${1 \over 8}$$ respectively. if all hit at the target independently, then the probability that the target would be hit, is :
Answer
(A)
$${{25} \over {32}}$$
15
Let $$\alpha $$ and $$\beta $$ be the roots of the equation x2 + x + 1 = 0. Then for y $$ \ne $$ 0 in R,
$$$\left| {\matrix{ {y + 1} & \alpha & \beta \cr \alpha & {y + \beta } & 1 \cr \beta & 1 & {y + \alpha } \cr } } \right|$$$ is equal to
Answer
(C)
y3
16
The area (in sq. units) of the region

A = {(x, y) : x2 $$ \le $$ y $$ \le $$ x + 2} is
Answer
(D)
$${{9 \over 2}}$$
17
Let the sum of the first n terms of a non-constant A.P., a1, a2, a3, ..... be $$50n + {{n(n - 7)} \over 2}A$$, where A is a constant. If d is the common difference of this A.P., then the ordered pair (d, a50) is equal to
Answer
(C)
(A, 50+46A)
18
The integral $$\int {{\rm{se}}{{\rm{c}}^{{\rm{2/ 3}}}}\,{\rm{x }}\,{\rm{cose}}{{\rm{c}}^{{\rm{4 / 3}}}}{\rm{x \,dx}}} $$ is equal to (Hence C is a constant of integration)
Answer
(D)
- 3tan–1/3x + C
19
The solution of the differential equation

$$x{{dy} \over {dx}} + 2y$$ = x2 (x $$ \ne $$ 0) with y(1) = 1, is :
Answer
(C)
$$y = {{{x^2}} \over 4} + {3 \over {4{x^2}}}$$
20
If the fourth term in the binomial expansion of $${\left( {{2 \over x} + {x^{{{\log }_8}x}}} \right)^6}$$ (x > 0) is 20 × 87, then a value of x is :
Answer
(B)
82
21
A committee of 11 members is to be formed from 8 males and 5 females. If m is the number of ways the committee is formed with at least 6 males and n is the number of ways the committee is formed with at least 3 females, then :
Answer
(B)
m = n = 78
22
If the fourth term in the binomial expansion of $${\left( {{2 \over x} + {x^{{{\log }_8}x}}} \right)^6}$$ (x > 0) is 20 × 87, then a value of x is :
Answer
(B)
82