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Relations and Functions (Class 12)

JEE Main 2025 (Online) 28th January Evening ShiftMCQMedium📈 Topic in 22% papers+4−1
Ques. 1JEE Main 2025, 28 January (Evening Shift)

Let f: R - \0\ (- , 1) be a polynomial of degree 2, satisfying f(x)f ( 1x ) = f(x) + f ( 1x ). If f(K) = -2K, then the sum of squares of all possible values of K is:

  1. 9
  2. 1
  3. 6
  4. 7

Answer

(3) 6

Solution

Let g(x) = f(x) - 1. Then the given relation becomes

(g(x) + 1) (g ( 1x ) + 1 ) = g(x) + g ( 1x ) + 2

g(x) g ( 1x ) = 1

Let g(x) = ax2 + bx + c (a 0). Then (ax2 + bx + c)(cx2 + bx + a) = x2 for all x.

The coefficient of x4 gives ac = 0, so c = 0; the coefficient of x3 gives ab + bc = 0, so b = 0; and the coefficient of x2 gives a2 = 1. Hence f(x) = 1 x2, and the range (- , 1), f(x) = 1 - x2.

Now f(K) = -2K gives

1 - K2 = -2K

K2 - 2K - 1 = 0 (K = 1 2, both non-zero)

K1 + K2 = 2, K1K2 = -1

K12 + K22 = (K1 + K2)2 - 2K1K2 = 4 + 2 = 6

Answer: (3)

Keep practising — Relations and Functions (Class 12)

Ques. 2JEE Main 2025, 28 January (Evening Shift)

Let f : [0, 3] A be defined by f(x) = 2x3 - 15x2 + 36x + 7 and g : [0, ) B be defined by g(x) = x2025x2025 + 1. If both the functions are onto and S = \x Z; x A or x B\, then n(S) is equal to :

  1. 29
  2. 31
  3. 30
  4. 36
Ques. 3JEE Main 2025, 24 January (Morning Shift)

Let f:R-\0\ be a function such that f(x)-6f ( 1x )= 353x- 52. If x 0 ( 1 x+f(x) )= ; , , then +2 is equal to

  1. 6
  2. 5
  3. 3
  4. 4
Ques. 4JEE Main 2025, 24 January (Morning Shift)

Let f(x)= 2x+2+1622x+1+2x+4+32. Then the value of 8 (f ( 115 )+f ( 215 )+ +f ( 5915 ) ) is equal to

  1. 108
  2. 92
  3. 118
  4. 102
Ques. 5JEE Main 2025, 24 January (Evening Shift)

The function f:(- , ) (- ,1), defined by f(x)= 2x-2-x2x+2-x is :

  1. One-one but not onto
  2. Onto but not one-one
  3. Both one-one and onto
  4. Neither one-one nor onto
Ques. 6JEE Main 2025, 24 January (Evening Shift)

Number of functions f:\1,2, ,100\ \0,1\, that assign 1 to exactly one of the positive integers less than or equal to 98, is equal to .

Ques. 7JEE Main 2025, 23 January (Morning Shift)

Let R=\(1,2),(2,3),(3,3)\ be a relation defined on the set \1,2,3,4\. Then the minimum number of elements, needed to be added in R so that R becomes an equivalence relation, is:

  1. 9
  2. 8
  3. 7
  4. 10
Ques. 8JEE Main 2025, 23 January (Evening Shift)

Let X=R . Define a relation R on X as : (a1,b1)R(a2,b2) b1=b2 In the light of the above statements, choose the correct answer from the options given below :

  1. Both Statement I and Statement II are true
  2. Statement I is true but Statement II is false
  3. Both Statement I and Statement II are false
  4. Statement I is false but Statement II is true
Ques. 9JEE Main 2025, 22 January (Morning Shift)

Let f(x) be a real differentiable function such that f(0)=1 and f(x+y)=f(x)f'(y)+f'(x)f(y) for all x,y . Then n=1100 ef(n) is equal to :

  1. 2406
  2. 5220
  3. 2525
  4. 2384
Ques. 10JEE Main 2025, 22 January (Morning Shift)

The number of non-empty equivalence relations on the set \1,2,3\ is :

  1. 7
  2. 4
  3. 5
  4. 6
Ques. 11JEE Main 2025, 22 January (Evening Shift)

Let A=\1,2,3,4\ and B=\1,4,9,16\. Then the number of many-one functions f:A B such that 1 f(A) is equal to :

  1. 151
  2. 139
  3. 163
  4. 127

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