Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Sets and Relations question

2019 · 12 Jan · Shift 2 · Q40
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Main
  3. /Mathematics
  4. /Sets and Relations
  5. /2019 · 12 Jan · Shift 2 · Q40

Sets and Relations question

2019 · 12 Jan · Shift 2 · Q40

JEE MainMathematicsSets and RelationsMCQ+4 / −1
Let Z be the set of integers. If A = {x ∈\in∈ Z : 2(x + 2) (x2 −-− 5x + 6) = 1} and B = {x ∈\in∈ Z : −-− 3 < 2x −-− 1 < 9}, then the number of subsets of the set A ×\times× B, is
  1. A
    212
  2. B
    218
  3. C
    210
  4. D
    215
View written solutionFree

Correct answer: 1

  1. Find set AAA

Given A={x∈Z:2(x+2)(x2−5x+6)=1}.A = \{x \in \mathbb{Z} : 2(x+2)(x^2-5x+6)=1\}.A={x∈Z:2(x+2)(x2−5x+6)=1}.

Since x∈Zx \in \mathbb{Z}x∈Z, the left-hand side 2(x+2)(x2−5x+6)2(x+2)(x^2-5x+6)2(x+2)(x2−5x+6) is an even integer, because it has a factor 222.

But the equation says 2(x+2)(x2−5x+6)=1,2(x+2)(x^2-5x+6)=1,2(x+2)(x2−5x+6)=1, and 111 is odd. An even integer can never equal 111.

Hence, there is no integer solution.

So, A=∅.A=\varnothing.A=∅.


  1. Find set BBB

Given B={x∈Z:−3<2x−1<9}.B = \{x \in \mathbb{Z} : -3 < 2x-1 < 9\}.B={x∈Z:−3<2x−1<9}.

Solve the double inequality: −3<2x−1<9.-3 < 2x-1 < 9.−3<2x−1<9.

Add 111 throughout: −2<2x<10.-2 < 2x < 10.−2<2x<10.

Divide by 222: −1<x<5.-1 < x < 5.−1<x<5.

Since x∈Zx \in \mathbb{Z}x∈Z, x=0,1,2,3,4.x=0,1,2,3,4.x=0,1,2,3,4.

Therefore, B={0,1,2,3,4},∣B∣=5.B=\{0,1,2,3,4\}, \quad |B|=5.B={0,1,2,3,4},∣B∣=5.


  1. Find A×BA \times BA×B

We know that A=∅.A=\varnothing.A=∅.

Therefore, A×B=∅×B=∅.A \times B = \varnothing \times B = \varnothing.A×B=∅×B=∅.

So, ∣A×B∣=0.|A \times B|=0.∣A×B∣=0.


  1. Number of subsets of A×BA \times BA×B

A set with nnn elements has 2n2^n2n subsets.

Here n=0n=0n=0, so number of subsets is 20=1.2^0=1.20=1.


  1. Compare with options

The derived answer is 1,1,1, which does not match any of the given options 212,218,210,2152^{12}, 2^{18}, 2^{10}, 2^{15}212,218,210,215 (written in the prompt as 212, 218, 210, 215).

This suggests there is likely a typo in the question statement for set AAA.

If the intended condition for AAA were something else, then the stored answer 2152^{15}215 would correspond to ∣A×B∣=15.|A\times B|=15.∣A×B∣=15. Since ∣B∣=5|B|=5∣B∣=5, this would require ∣A∣=3|A|=3∣A∣=3. But with the given equation 2(x+2)(x2−5x+6)=12(x+2)(x^2-5x+6)=12(x+2)(x2−5x+6)=1, we definitely get A=∅A=\varnothingA=∅.

So the stored answer cannot be correct for the question as written.

PreviousNext

More from Sets and Relations

  • Consider the following two binary relations on the set A = {a, b, c} : R1 = {(c, a), (b, b), (a, c), (c, c), (b, c), (a, a)} and R2 = {(a, b), (b, a), (c, c), (c, a), (a, a), (b, b), (a, c)}. Then :2018 · MCQ
  • Let N denote the set of all natural numbers. Define two binary relations on N as R = {(x, y) ∈ N × N : 2x + y = 10} and R2 = {(x, y) ∈ N × N : x + 2y = 10}. Then :2018 · MCQ
  • Two sets A and B are as under : A = {(a, b) ∈ R × R : |a - 5| < 1 and |b - 5| < 1}; B = {(a, b) ∈ R × R : 4(a- 6)2 + 9(b - 5)2 ≤ 36 }; Then2018 · MCQ
  • Let P = {θ : sin θ− cos θ=2​cosθ} and Q = {θ : sin θ + cos θ=2​sinθ} be two sets. Then2016 · MCQ
  • Let A and B be two sets containing four and two elements respectively. Then, the number of subsets of the set A × B , each having atleast three elements are2015 · MCQ
  • Let X = {1, 2, 3, 4, 5}. The number of different ordered pairs (Y, Z) that can be formed such that Y ⊆ X, Z ⊆ X and Y ∩ Z is empty, is :2012 · MCQ
  • Let R be the set of real numbers. Statement I : A={(x,y)∈R×R:y−x is an integer } is an equivalence relation on R. Statement II : B={(x,y)∈R×R:x=αy for some rational number α} is an…2011 · MCQ
  • Consider the following relations R={(x,y)∣x,y are real numbers and x=wy for some rational number w}; S={(nm​,qp​)∣m,n,p and q are integers such that n,qeq0 and qm=pm}…2010 · MCQ