JEE MAIN - Mathematics (2021 - 18th March Morning Shift)

• 1

  The number of integral values of m so that the abscissa of point of intersection of lines 3x + 4y = 9 and y = mx + 1 is also an integer, is :

  답변

  (B)

  2
• 2

  The solutions of the equation $$\left| {\matrix{ {1 + {{\sin }^2}x} & {{{\sin }^2}x} & {{{\sin }^2}x} \cr {{{\cos }^2}x} & {1 + {{\cos }^2}x} & {{{\cos }^2}x} \cr {4\sin 2x} & {4\sin 2x} & {1 + 4\sin 2x} \cr } } \right| = 0,(0 < x < \pi )$$, are

  답변

  (D)

  $${{7\pi } \over {12}},{{11\pi } \over {12}}$$
• 3

  Let $$\alpha$$, $$\beta$$, $$\gamma$$ be the real roots of the equation, x³ + ax² + bx + c = 0, (a, b, c $$\in$$ R and a, b $$\ne$$ 0). If the system of equations (in u, v, w) given by $$\alpha$$u + $$\beta$$v + $$\gamma$$w = 0, $$\beta$$u + $$\gamma$$v + $$\alpha$$w = 0; $$\gamma$$u + $$\alpha$$v + $$\beta$$w = 0 has non-trivial solution, then the value of $${{{a^2}} \over b}$$ is

  답변

  (B)

  3
• 4

  The integral $$\int {{{(2x - 1)\cos \sqrt {{{(2x - 1)}^2} + 5} } \over {\sqrt {4{x^2} - 4x + 6} }}} dx$$ is equal to (where c is a constant of integration)

  답변

  (A)

  $${1 \over 2}\sin \sqrt {{{(2x - 1)}^2} + 5} + c$$
• 5

  The equation of one of the straight lines which passes through the point (1, 3) and makes an angles $${\tan ^{ - 1}}\left( {\sqrt 2 } \right)$$ with the straight line, y + 1 = 3$${\sqrt 2 }$$ x is :

  답변

  (A)

  $$4\sqrt 2 x + 5y - \left( {15 + 4\sqrt 2 } \right) = 0$$
• 6

  If $$\mathop {\lim }\limits_{x \to 0} {{{{\sin }^{ - 1}}x - {{\tan }^{ - 1}}x} \over {3{x^3}}}$$ is equal to L, then the value of (6L + 1) is

  답변

  (D)

  2
• 7

  A vector $$\overrightarrow a $$ has components 3p and 1 with respect to a rectangular cartesian system. This system is rotated through a certain angle about the origin in the counter clockwise sense. If, with respect to new system, $$\overrightarrow a $$ has components p + 1 and $$\sqrt {10} $$, then the value of p is equal to :

  답변

  (D)

  $$-$$1
• 8

  If the equation $$a|z{|^2} + \overline {\overline \alpha z + \alpha \overline z } + d = 0$$ represents a circle where a, d are real constants then which of the following condition is correct?

  답변

  (B)

  |$$\alpha$$|² $$-$$ ad > 0 and a$$\in$$R $$-$$ {0}
• 9

  For the four circles M, N, O and P, following four equations are given :
  
  Circle M : x² + y² = 1
  
  Circle N : x² + y² $$-$$ 2x = 0
  
  Circle O : x² + y² $$-$$ 2x $$-$$ 2y + 1 = 0
  
  Circle P : x² + y² $$-$$ 2y = 0
  
  If the centre of circle M is joined with centre of the circle N, further center of circle N is joined with centre of the circle O, centre of circle O is joined with the centre of circle P and lastly, centre of circle P is joined with centre of circle M, then these lines form the sides of a :

  답변

  (B)

  Square
• 10

  The real valued function
  $$f(x) = {{\cos e{c^{ - 1}}x} \over {\sqrt {x - [x]} }}$$, where [x] denotes the greatest integer less than or equal to x, is defined for all x belonging to :

  답변

  (B)

  all non-integers except the interval [ $$-$$1, 1 ]
• 11

  If the functions are defined as $$f(x) = \sqrt x $$ and $$g(x) = \sqrt {1 - x} $$, then what is the common domain of the following functions :
  
  f + g, f $$-$$ g, f/g, g/f, g $$-$$ f where $$(f \pm g)(x) = f(x) \pm g(x),(f/g)x = {{f(x)} \over {g(x)}}$$

  답변

  (C)

  $$0 < x < 1$$
• 12

  If $$f(x) = \left\{ {\matrix{ {{1 \over {|x|}}} & {;\,|x|\, \ge 1} \cr {a{x^2} + b} & {;\,|x|\, < 1} \cr } } \right.$$ is differentiable at every point of the domain, then the values of a and b are respectively :

  답변

  (D)

  $$ - {1 \over 2},{3 \over 2}$$
• 13

  Let $$A + 2B = \left[ {\matrix{ 1 & 2 & 0 \cr 6 & { - 3} & 3 \cr { - 5} & 3 & 1 \cr } } \right]$$ and $$2A - B = \left[ {\matrix{ 2 & { - 1} & 5 \cr 2 & { - 1} & 6 \cr 0 & 1 & 2 \cr } } \right]$$. If Tr(A) denotes the sum of all diagonal elements of the matrix A, then Tr(A) $$-$$ Tr(B) has value equal to

  답변

  (B)

  2
• 14

  The sum of all the 4-digit distinct numbers that can be formed with the digits 1, 2, 2 and 3 is :

  답변

  (A)

  26664
• 15

  The value of $$3 + {1 \over {4 + {1 \over {3 + {1 \over {4 + {1 \over {3 + ....\infty }}}}}}}}$$ is equal to

  답변

  (A)

  1.5 + $$\sqrt 3 $$
• 16

  The number of times the digit 3 will be written when listing the integers from 1 to 1000 is :

  답변

  300
• 17

  Let f(x) and g(x) be two functions satisfying f(x²) + g(4 $$-$$ x) = 4x³ and g(4 $$-$$ x) + g(x) = 0, then the value of $$\int\limits_{ - 4}^4 {f{{(x)}^2}dx} $$ is

  답변

  512
• 18

  The missing value in the following figure is
  
  

  답변

  4
• 19

  Let z₁, z₂ be the roots of the equation z² + az + 12 = 0 and z₁, z₂ form an equilateral triangle with origin. Then, the value of |a| is :

  답변

  6
• 20

  The mean age of 25 teachers in a school is 40 years. A teacher retires at the age of 60 years and a new teacher is appointed in his place. If the mean age of the teachers in this school now is 39 years, then the age (in years) of the newly appointed teacher is _________.

  답변

  35
• 21

  If $$f(x) = \int {{{5{x^8} + 7{x^6}} \over {{{({x^2} + 1 + 2{x^7})}^2}}}dx,(x \ge 0),f(0) = 0} $$ and $$f(1) = {1 \over K}$$, then the value of K is

  답변

  4
• 22

  A square ABCD has all its vertices on the curve x²y² = 1. The midpoints of its sides also lie on the same curve. Then, the square of area of ABCD is _________.

  답변

  80