JEE MAIN - Mathematics (2020 - 8th January Morning Slot)

1
The least positive value of 'a' for which the equation

2x2 + (a – 10)x + $${{33} \over 2}$$ = 2a has real roots is
Answer
8
2
The number of all 3 × 3 matrices A, with enteries from the set {–1, 0, 1} such that the sum of the diagonal elements of AAT is 3, is
Answer
672
3
The shortest distance between the lines

$${{x - 3} \over 3} = {{y - 8} \over { - 1}} = {{z - 3} \over 1}$$ and

$${{x + 3} \over { - 3}} = {{y + 7} \over 2} = {{z - 6} \over 4}$$ is :
Answer
(C)
$$3\sqrt {30} $$
4
Let ƒ(x) = xcos–1(–sin|x|), $$x \in \left[ { - {\pi \over 2},{\pi \over 2}} \right]$$, then which of the following is true?
Answer
(A)
ƒ' is decreasing in $$\left( { - {\pi \over 2},0} \right)$$ and increasing in $$\left( {0,{\pi \over 2}} \right)$$
5
The shortest distance between the lines

$${{x - 3} \over 3} = {{y - 8} \over { - 1}} = {{z - 3} \over 1}$$ and

$${{x + 3} \over { - 3}} = {{y + 7} \over 2} = {{z - 6} \over 4}$$ is :
Answer
(C)
$$3\sqrt {30} $$
6
Let ƒ(x) = xcos–1(–sin|x|), $$x \in \left[ { - {\pi \over 2},{\pi \over 2}} \right]$$, then which of the following is true?
Answer
(A)
ƒ' is decreasing in $$\left( { - {\pi \over 2},0} \right)$$ and increasing in $$\left( {0,{\pi \over 2}} \right)$$
7
The inverse function of

f(x) = $${{{8^{2x}} - {8^{ - 2x}}} \over {{8^{2x}} + {8^{ - 2x}}}}$$, x $$ \in $$ (-1, 1), is :
Answer
(C)
$${1 \over 4}\left( {{{\log }_8}e} \right){\log _e}\left( {{{1 + x} \over {1 - x}}} \right)$$
8
If $$\int {{{\cos xdx} \over {{{\sin }^3}x{{\left( {1 + {{\sin }^6}x} \right)}^{2/3}}}}} = f\left( x \right){\left( {1 + {{\sin }^6}x} \right)^{1/\lambda }} + c$$

where c is a constant of integration, then $$\lambda f\left( {{\pi \over 3}} \right)$$ is equal to
Answer
(C)
-2
9
The locus of a point which divides the line segment joining the point (0, –1) and a point on the parabola, x2 = 4y, internally in the ratio 1 : 2, is :
Answer
(D)
9x2 – 12y = 8
10
For which of the following ordered pairs ($$\mu $$, $$\delta $$), the system of linear equations
x + 2y + 3z = 1
3x + 4y + 5z = $$\mu $$
4x + 4y + 4z = $$\delta $$
is inconsistent ?
Answer
(B)
(4, 3)
11
The mean and the standard deviation (s.d.) of 10 observations are 20 and 2 resepectively. Each of these 10 observations is multiplied by p and then reduced by q, where p $$ \ne $$ 0 and q $$ \ne $$ 0. If the new mean and new s.d. become half of their original values, then q is equal to
Answer
(B)
-20
12
For a > 0, let the curves C1 : y2 = ax and C2 : x2 = ay intersect at origin O and a point P. Let the line x = b (0 < b < a) intersect the chord OP and the x-axis at points Q and R, respectively. If the line x = b bisects the area bounded by the curves, C1 and C2, and the area of
$$\Delta $$OQR = $${1 \over 2}$$, then 'a' satisfies the equation :
Answer
(A)
x6 – 12x3 + 4 = 0
13
If the equation, x2 + bx + 45 = 0 (b $$ \in $$ R) has conjugate complex roots and they satisfy |z +1| = 2$$\sqrt {10} $$ , then :
Answer
(D)
b2 – b = 30
14
Let two points be A(1, –1) and B(0, 2). If a point P(x', y') be such that the area of $$\Delta $$PAB = 5 sq. units and it lies on the line, 3x + y – 4$$\lambda $$ = 0, then a value of $$\lambda $$ is :
Answer
(D)
3
15
Let y = y(x) be a solution of the differential equation,

$$\sqrt {1 - {x^2}} {{dy} \over {dx}} + \sqrt {1 - {y^2}} = 0$$, |x| < 1.

If $$y\left( {{1 \over 2}} \right) = {{\sqrt 3 } \over 2}$$, then $$y\left( { - {1 \over {\sqrt 2 }}} \right)$$ is equal to :
Answer
(C)
$${{1 \over {\sqrt 2 }}}$$
16
$$\mathop {\lim }\limits_{x \to 0} {\left( {{{3{x^2} + 2} \over {7{x^2} + 2}}} \right)^{{1 \over {{x^2}}}}}$$ is equal to
Answer
(C)
$${1 \over {{e^2}}}$$
17
Let ƒ(x) = (sin(tan–1x) + sin(cot–1x))2 – 1, |x| > 1.
If $${{dy} \over {dx}} = {1 \over 2}{d \over {dx}}\left( {{{\sin }^{ - 1}}\left( {f\left( x \right)} \right)} \right)$$ and $$y\left( {\sqrt 3 } \right) = {\pi \over 6}$$, then y($${ - \sqrt 3 }$$) is equal to :
Answer
(B)
$$ - {\pi \over 6}$$
18
Let ƒ : R $$ \to $$ R be such that for all x $$ \in $$ R
(21+x + 21–x), ƒ(x) and (3x + 3–x) are in A.P.,
then the minimum value of ƒ(x) is
Answer
(C)
3
19
If a, b and c are the greatest value of 19Cp, 20Cq and 21Cr respectively, then :
Answer
(D)
$${a \over {11}} = {b \over {22}} = {c \over {42}}$$