NEED HELP DUE IN 2 MINUTES!!!!

For x, y ∈ R we write x ∼ y if x − y is an integer. a) Show that ∼ is an equivalence relation on R. b) Show that the set [0, 1)

vodomira [7]

Answer:

A. It is an equivalence relation on R

B. In fact, the set [0,1) is a set of representatives

Step-by-step explanation:

A. The definition of an equivalence relation demands 3 things:

The relation being reflexive (∀a∈R, a∼a)
The relation being symmetric (∀a,b∈R, a∼b⇒b∼a)
The relation being transitive (∀a,b,c∈R, a∼b^b∼c⇒a∼c)

And the relation ∼ fills every condition.

∼ is Reflexive:

Let a ∈ R

it´s known that a-a=0 and because 0 is an integer

a∼a, ∀a ∈ R.

∼ is Reflexive by definition

∼ is Symmetric:

Let a,b ∈ R and suppose a∼b

a∼b ⇒ a-b=k, k ∈ Z

b-a=-k, -k ∈ Z

b∼a, ∀a,b ∈ R

∼ is Symmetric by definition

∼ is Transitive:

Let a,b,c ∈ R and suppose a∼b and b∼c

a-b=k and b-c=l, with k,l ∈ Z

(a-b)+(b-c)=k+l

a-c=k+l with k+l ∈ Z

a∼c, ∀a,b,c ∈ R

∼ is Transitive by definition

We´ve shown that ∼ is an equivalence relation on R.

B. Now we have to show that there´s a bijection from [0,1) to the set of all equivalence classes (C) in the relation ∼.

Let F: [0,1) ⇒ C a function that goes as follows: F(x)=[x] where [x] is the class of x.

Now we have to prove that this function F is injective (∀x,y∈[0,1), F(x)=F(y) ⇒ x=y) and surjective (∀b∈C, Exist x such that F(x)=b):

F is injective:

let x,y ∈ [0,1) and suppose F(x)=F(y)

[x]=[y]

x ∈ [y]

x-y=k, k ∈ Z

x=k+y

because x,y ∈ [0,1), then k must be 0. If it isn´t, then x ∉ [0,1) and then we would have a contradiction

x=y, ∀x,y ∈ [0,1)

F is injective by definition

F is surjective:

Let b ∈ R, let´s find x such as x ∈ [0,1) and F(x)=[b]

Let c=║b║, in other words the whole part of b (c ∈ Z)

Set r as b-c (let r be the decimal part of b)

r=b-c and r ∈ [0,1)

Let´s show that r∼b

r=b-c ⇒ c=b-r and because c ∈ Z

r∼b

[r]=[b]

F(r)=[b]

∼ is surjective

Then F maps [0,1) into C, i.e [0,1) is a set of representatives for the set of the equivalence classes.

4 0

3 years ago

X + y = 3

Studentka2010 [4]

Answer:

Infinitely many solutions

Step-by-step explanation:

x+y=3

2x+2y=6

x=3-y

2(3-y)+2y=6

6-2y+2y=6

6+0=6

6=6

infinitely many solutions

3 0

3 years ago

Which of the two circles in this figure is larger?<br><br> A Shape and Lines

faltersainse [42]

Answer: Shapes

Step-by-step explanation: Lines is simple and soft, Shapes is sharp and hard

6 0

3 years ago

Please Help me!!!

drek231 [11]

Step-by-step explanation:

The displacement of a particle d (in km) as a function of time t (in hours) is given by :

$d=2t^3+5t^2-3$

Displacement at t = 4 hours,

$d(4)=2(4)^3+5(4)^2-3=205\ km$

Velocity of particle is given by :

$v=\dfrac{dd}{dt}\\\\v=\dfrac{d(2t^3+5t^2-3)}{dt}\\\\v=6t^2+10t$

Velocity at t = 4 hours,

$v=6(4)^2+10(4)=136\ km/h$

Acceleration of the particle is given by :

$a=\dfrac{dv}{dt}\\\\a=\dfrac{d(6t^2+10t)}{dt}\\\\a=12t+10$

At t = 4 hours,

$a=12(4)+10=58\ km/h^2$

Therefore, the displacement, velocity and acceleration at t = 4 hours is 205 km, 136 km/h and 58 km/h² respectively.

7 0

3 years ago

Mrs. Gomes found that 40% of students at her high school take chemistry. She randomly surveys 12 students. What is the probabili

zlopas [31]

Answer:

The correct answer to the following question will be "0.438".

Step-by-step explanation:

Just because Mrs. Gomes finds around 40% of students in herself high school are studying chemistry.

Although each student becomes independent of one another, we may conclude:

"x" number of the students taking chemistry seems to be binomial to p = constant probability = 0.40

Given:

Number of surveys

= 12

Exactly 4 students have taken chemistry:

$=P(X\leq4)$

$=P(x=0)+P(x=1)+P(x=2)+P(x=3)+P(x=4)$

$=\Sigma_{0}^{4} C_{r}(0.4)^r(0.6)^{12-r}$

On substituting the above equation, we get the probability of approximately "0.438".

So that the above would be the appropriate answer.

5 0

3 years ago