Representation of the set of {2,3,5,7} by description This is the fourth sub problem of the third problem of Exercise 1.1 in the mathematics 1.1 set and its representation of Shanghai senior one,

Representation of the set of {2,3,5,7} by description This is the fourth sub problem of the third problem of Exercise 1.1 in the mathematics 1.1 set and its representation of Shanghai senior one,

{x | x is prime, X ≤ 7}

Express the set {- 1 / 2,2 / 3, - 3 / 4.} in a descriptive way!

{-1/2,2/3,-3/4.}
={(- 1) ^ n * n / (n + 1) | n belongs to the set of natural numbers}

The set {1,4,9,16} is represented by description
My answer is {x | x = 1 or 4 or 9 or 16}
The reference answer is {x | x = n ^ 2, n = 1,2,3,4}
If I'm wrong, how can I be wrong?

It's all right in the right way
But you don't understand the subject
They asked you to use descriptive method, not enumeration method. The child is so good-looking, the book = = I recently our teacher is also teaching this

Add three and a quarter to a number and subtract five and a half. The result is six and a third
2. The circumference of a triangle is 18 cm, of which the two sides are five and three-quarters cm and seven and one sixth cm respectively. Then what is the length of the third side?
3. The turnover of a shopping mall in January was 23.3 and 30.4 million yuan. The turnover in February was 2.5 million yuan less than that in January. How many million yuan is the total turnover of this shopping mall in two months?
Four solutions to the equation x + 5 and one-half = 6 and two-thirds + two and four fifths
A number plus the sum of three ninths and two fifths equals two fifths and eight fifths

The result is six and one-third. Find this number (process) 6 and 1 / 3 + 5 and 1 / 2-3 and 3 / 4 = (6 + 5-3) + (1 / 3 + 1 / 2-3 / 4) = 8 + 1 / 12 = 8 and 1 / 12. The perimeter of the triangle is 18 cm, and the two sides are 5 and 3 / 4 cm and

One half of a number is six times more than one third of it. What's 25% of the number

This number is 6 / (1 / 2-1 / 3) = 36
Twenty five percent of this number is 36 * 0.25 = 9

The quotient of two numbers is three and one-half. One of them is two and one-third. What's the other number?

49 / 6 or 2 / 3

Fill the bottle with a bottle of water, pour out 1 / 2 of all the water, and then pour in the same amount of alcohol, pour out 1 / 3 of all the solution, and then fill it with alcohol, and then
Fill the bottle with a bottle of water, pour out 1 / 2 of all the water, then pour in the same amount of milk, pour out 1 / 3 of all the solution, fill it with milk, then pour out 1 / 4 of all the solution, fill it with milk, finally pour out 1 / 5 of all the solution, fill it with milk, then what percentage of the total solution is milk

[title] fill a bottle with water, pour out 1 / 2 of all the water, then pour in the same amount of milk, pour out 1 / 3 of all the solution, fill it with milk, then pour out 1 / 4 of all the solution, fill it with milk, finally pour out 1 / 5 of all the solution, fill it with milk, then what percentage of the total solution is milk
Check the amount of water left each time, and then count the milk content
For the first time, 1-1 / 2 = 1 / 2 water was left
The second time left 1 / 2 × (1-1 / 3) = 1 / 3 of water
The third time left 1 / 3 × (1-1 / 4) = 1 / 4 of water
The fourth time left 1 / 4 × (1-1 / 5) = 1 / 5 of water
At this time, milk accounts for 1-1 / 5 of the total solution = 80%

Fill a container with water, pour out half of all the water, then fill it with the same amount of alcohol, mix it, pour out one third of all the solution, and then use it again
Then fill it with alcohol. After mixing, pour out a quarter of the total solution, and then fill it with alcohol. What is the percentage of the total solution in the alcohol station?

General formula: 1 / 2 (1 + 1 / 3 + 1 / 4 +) +1/n)

Fill the bottle with a bottle of water, pour out 12% of all the water, then pour in the same amount of alcohol, pour out 13% of all the solution, fill it with alcohol, then pour out 14% of all the solution, and fill it with alcohol, then the alcohol accounts for 30% of all the solution______ %．

1-12 = 12; 12 × (1-13) = 13; 13 × (1-14) = 14; 1-14 = 34.34 × 100% = 75%

Fill the bottle with a bottle of water, pour out 12% of all the water, then pour in the same amount of alcohol, pour out 13% of all the solution, fill it with alcohol, then pour out 14% of all the solution, and fill it with alcohol, then the alcohol accounts for 30% of all the solution______ %．

1-12 = 12; 12 × (1-13) = 13; 13 × (1-14) = 14; 1-14 = 34.34 × 100% = 75%