JEE MAIN - Mathematics (2020 - 2nd September Evening Slot)

1
Let a, b, c $$ \in $$ R be all non-zero and satisfy
a3 + b3 + c3 = 2. If the matrix

A = $$\left( {\matrix{ a & b & c \cr b & c & a \cr c & a & b \cr } } \right)$$

satisfies ATA = I, then a value of abc can be :
Answer
(B)
$${1 \over 3}$$
2
If the equation cos4 $$\theta $$ + sin4 $$\theta $$ + $$\lambda $$ = 0 has real solutions for $$\theta $$, then $$\lambda $$ lies in the interval :
Answer
(D)
$$\left[ { - 1, - {1 \over 2}} \right]$$
3
Let f : R $$ \to $$ R be a function which satisfies
f(x + y) = f(x) + f(y) $$\forall $$ x, y $$ \in $$ R. If f(1) = 2 and
g(n) = $$\sum\limits_{k = 1}^{\left( {n - 1} \right)} {f\left( k \right)} $$, n $$ \in $$ N then the value of n, for which g(n) = 20, is :
Answer
(C)
5
4
Let f(x) be a quadratic polynomial such that
f(–1) + f(2) = 0. If one of the roots of f(x) = 0
is 3, then its other root lies in :
Answer
(C)
(–1, 0)
5
Let n > 2 be an integer. Suppose that there are n Metro stations in a city located along a circular path. Each pair of stations is connected by a straight track only. Further, each pair of nearest stations is connected by blue line, whereas all remaining pairs of stations are connected by red line. If the number of red lines is 99 times the number of blue lines, then the value of n is :
Answer
(A)
201
6
The area (in sq. units) of an equilateral triangle inscribed in the parabola y2 = 8x, with one of its vertices on the vertex of this parabola, is :
Answer
(D)
$$192\sqrt 3 $$
7
Let f : (–1, $$\infty $$) $$ \to $$ R be defined by f(0) = 1 and
f(x) = $${1 \over x}{\log _e}\left( {1 + x} \right)$$, x $$ \ne $$ 0. Then the function f :
Answer
(A)
decreases in (–1, $$\infty $$)
8
Let A = {X = (x, y, z)T: PX = 0 and

x2 + y2 + z2 = 1} where

$$P = \left[ {\matrix{ 1 & 2 & 1 \cr { - 2} & 3 & { - 4} \cr 1 & 9 & { - 1} \cr } } \right]$$,

then the set A :
Answer
(C)
contains exactly two elements.
9
Let the position vectors of points 'A' and 'B' be
$$\widehat i + \widehat j + \widehat k$$ and $$2\widehat i + \widehat j + 3\widehat k$$, respectively. A point 'P' divides the line segment AB internally in the ratio $$\lambda $$ : 1 ( $$\lambda $$ > 0). If O is the origin and
$$\overrightarrow {OB} .\overrightarrow {OP} - 3{\left| {\overrightarrow {OA} \times \overrightarrow {OP} } \right|^2} = 6$$, then $$\lambda $$ is equal to______.
Answer
0.8
10
Let [t] denote the greatest integer less than or equal to t.
Then the value of $$\int\limits_1^2 {\left| {2x - \left[ {3x} \right]} \right|dx} $$ is ______.
Answer
1
11
If y = $$\sum\limits_{k = 1}^6 {k{{\cos }^{ - 1}}\left\{ {{3 \over 5}\cos kx - {4 \over 5}\sin kx} \right\}} $$,

then $${{dy} \over {dx}}$$ at x = 0 is _______.
Answer
91
12
If the variance of the terms in an increasing A.P.,
b1 , b2 , b3 ,....,b11 is 90, then the common difference of this A.P. is_______.
Answer
3
13
If the variance of the terms in an increasing A.P.,
b1 , b2 , b3 ,....,b11 is 90, then the common difference of this A.P. is_______.
Answer
3
14
The set of all possible values of $$\theta $$ in the interval
(0, $$\pi $$) for which the points (1, 2) and (sin $$\theta $$, cos $$\theta $$) lie
on the same side of the line x + y = 1 is :
Answer
(D)
$$\left( {0,{\pi \over 2}} \right)$$
15
If a curve y = f(x), passing through the point (1, 2), is the solution of the differential equation,
2x2dy= (2xy + y2)dx, then $$f\left( {{1 \over 2}} \right)$$ is equal to :
Answer
(B)
$${1 \over {1 + {{\log }_e}2}}$$
16
Consider a region R = {(x, y) $$ \in $$ R : x2 $$ \le $$ y $$ \le $$ 2x}. if a line y = $$\alpha $$ divides the area of region R into two equal parts, then which of the following is true?
Answer
(C)
3$$\alpha $$2 - 8$$\alpha $$3/2 + 8 = 0
17
For some $$\theta \in \left( {0,{\pi \over 2}} \right)$$, if the eccentricity of the
hyperbola, x2–y2sec2$$\theta $$ = 10 is $$\sqrt 5 $$ times the
eccentricity of the ellipse, x2sec2$$\theta $$ + y2 = 5, then the length of the latus rectum of the ellipse, is :
Answer
(C)
$${{4\sqrt 5 } \over 3}$$
18
$$\mathop {\lim }\limits_{x \to 0} {\left( {\tan \left( {{\pi \over 4} + x} \right)} \right)^{{1 \over x}}}$$ is equal to :
Answer
(D)
$$e$$2
19
The imaginary part of
$${\left( {3 + 2\sqrt { - 54} } \right)^{{1 \over 2}}} - {\left( {3 - 2\sqrt { - 54} } \right)^{{1 \over 2}}}$$ can be :
Answer
(A)
-2$$\sqrt 6 $$
20
If the sum of first 11 terms of an A.P.,
a1, a2, a3, .... is 0 (a $$ \ne $$ 0), then the sum of the A.P.,
a1 , a3 , a5 ,....., a23 is ka1 , where k is equal to :
Answer
(D)
-$${{72} \over 5}$$