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never [62]
3 years ago
14

1. Prove or give a counterexample for the following statements: a) If ff: AA → BB is an injective function and bb ∈ BB, then |ff

−1({bb})| = 1. b) If ff: AA → BB is a bijection and AA is countable, then BB is countable. c) If ff: AA → BB is a surjective function and AA is finite, then BB is finite. d) If ff: AA → BB is a surjective function and BB is finite, then AA is finite.
Mathematics
1 answer:
Fantom [35]3 years ago
4 0

Answer:

a) False. A = {1}, B = {1,2} f: A ⇒ B, f(1) = 1

b) True

c) True

d) B = {1}, A = N, f: N ⇒ {1}, f(x) = 1

Step-by-step explanation:

a) lets use A = {1}, B = {1,2} f: A ⇒ B, f(1) = 1. Here f is injective but 2 is an element of b and |f−¹({b})| = 0., not 1. This statement is False.

b) This is True. If  A were finite, then it can only be bijective with another finite set with equal cardinal, therefore, B should be finite (and with equal cardinal). If A were not finite but countable, then there should exist a bijection g: N ⇒ A, where N is the set of natural numbers. Note that f o g : N ⇒ B is a bijection because it is composition of bijections. This, B should be countable. This statement is True.

c) This is true, if f were surjective, then for every element of B there should exist an element a in A such that f(a) = b. This means that  f−¹({b}) has positive cardinal for each element b from B. since f⁻¹(b) ∩ f⁻¹(b') = ∅ for different elements b and b' (because an element of A cant return two different values with f). Therefore, each element of B can be assigned to a subset of A (f⁻¹(b)), with cardinal at least 1, this means that |B| ≤ |A|, and as a consequence, B is finite.

b) This is false, B = {1} is finite, A = N is infinite, however if f: N ⇒ {1}, f(x) = 1 for any natural number x, then f is surjective despite A not being finite.

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The data shown has a least-squares regression line of y=3.2x−6.4.
Damm [24]

Answer:

1) B. on, 2) D. 19.2, 3) C. 0

Step-by-step explanation:

1) The value of y according to the regression line is:

y = 3.2\cdot (8) - 6.4

y = 19.2

Hence, the point (8,19.2) is <em>on </em>the least-squares regression line.

2) The value of y according to the regression line is 19.2.

3) The residual is the difference between the value from the regression line and the real value. In this case, the residual value is 0.

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3 years ago
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vampirchik [111]
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2 to the power of 4 x 2 to the power of 9 x 2
attashe74 [19]

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Solve for x and y 4x-3y=14,6x +y=-10​
Anna [14]

Answer:

y= -8/11   x=-63/11

Step-by-step explanation:

Rewrite equation

Step: Solve6x+y=−10for y

Step: Substitute−6x−10 for y in 4x−3y=14

Step: Substitute  −8 /11  for x in y=−6x−10

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___________________________________________

y= -8/11

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​Arif's backyard is 24 by 37 meters. He wants to put a flower garden in the middle of the​ backyard, leaving a strip of grass of
Tpy6a [65]

Answer:

Length of the flower garden = 29 meters

Width of the flower garden = 16 meters

Step-by-step explanation:

I have also attached a diagram for your convenience

Now First let us see the data we are given with:

Arif's backyard length = 37 meters

Arif's backyard Width = 24 meters

Area that should be left with grass = 424 m^2

Now lets suppose the width of the stirp of grass be "a"

According the image the area of backyard will be:

Area ABCD = 24 x 37

Area ABCD = 888 m^2

The length LM will be = (37 -2a)

The Width LO will be = (24 -2a)

Area LMNO = (37 -2a) x  (24 -2a)

Area LMNO = 888 -74a -48a +4a^2

Area LMNO = 4a^2 -122a + 888

Now in order the to calculate the area of the grass strip we must subtract the area LMNO from the total area ABCD and we already know that the areas the area of grass strip should be 424 m^2

hence, A = Area ABCD - Area LMNO

424 = 888 - (4a^2 -122a + 888)

424 = 888 - 4a^2 +122a - 888

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(We can solve this quadratic equation by breaking the middle term method)

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2(2x-53) = 0

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x = 4

Length of the flower garden = 37 -2(4)

Length of the flower garden = 29 meters

Width of the flower garden = 24 -2(4)

Width of the flower garden = 16 meters

4 0
3 years ago
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