Science and technology books account for 40% of the total books in the school library, and story books account for 30% of the total books. There are 1200 more science and technology books than story books?

A: there are 12000 books in the school library

The rational numbers a, B and C are known. As shown in the figure, we can simplify | a + B | - | C-A | - → C a 0b

When the absolute value of a is greater than that of B, the absolute value of a is greater than that of B,
|a+b|-|c-a| =b-a-a+c=b-2a+c.
When the absolute value of a is less than that of B and greater than,
|a+b|-|c-a| =a+b-a+c=b+c.

The denominator is an equal ratio sequence, and the numerator is an equal difference sequence. How to sum?
I want a mathematical solution-_ -TTT

Let the sum be a, let the common ratio of denominator be q.qa-a = a formula B, sort out formula B, and sum B (I believe you should be able to, which is almost the sum of equal ratio sequence), then a = B / Q-1 is done Get it

Let a be a constant, f (x) = x & # 178; + X + (x + 1) | x-a |
(1) When a = 0, find the range of function f (x)
(2) When x ≥ a, the inequality f (x) ≥ 0 is solved

1) A = 0, f (x) = x (x + 1) + (x + 1) | x | = (x + 1) (x + | x |) when x > = 0, there is f (x) = 2x (x + 1) = 2 [(x + 1 / 2) ^ 2-1 / 4] > = 0. When x = a, there is f (x) = x (x + 1) + (x + 1) (x-a) = (x + 1) (2x-a) > = 0. If a = - 1 or x = a, there is x > = - 1 or a = = a, so it is subdivided into: - 2

1. A and B are rational numbers to judge the relationship between | a + B |, | a | + | B |, | a | - | B |
2. Why is the square of 1 + 2 + 2 + the cube of 2 + +2 to the 63rd power = 2 to the 64th power - 1? Write the calculation process
3. The rational numbers a, B and C are not zero. Let x = |a | / B + C + |b | / C + A + |c | / A + B │, try to find the value of X to the 19th power + 99x + 2000
If the answer is detailed, I will offer a reward It's the first volume of junior high school

If a < 0, B < 0, then a-a-b, a-a-b, a-a-a-b, a-a-b, A-B, A-B, A-B, A-B, A-B, A-B, A-B, A-B, A-B, a-a-b, a-a-b, B-B, a-a-b, a-a-b, A-B, A-B, A-B, a-a-b, a-a-b, a-a-a-a-b, if a < 0, B ≥ 0, B ≥ 0, then a-a-a-a-a-a-a-a-a-a-b, a-a-a-a-a-a-b, a-a-a-a-a-a-a-a-a-a-a-b, a-a-a-a-a-a-b, a-a-a-a-a-a-a-a-a-a if | = - A-B, then | a + B | = | a | - | B | < a | + | B | if a ≥ 0, B < 0, the result is as above, if a ≥ 0, B ≥ 0, then | a + B | = | a | + | B |

There is a column of numbers, arranged according to a certain rule: - 1, 2, - 4, 8, - 16, 32, - 64 Is it true that the sum of three adjacent ones is 1224? Please give reasons

Let the middle number be (- 1) n × 2N-1, then the first number is (- 1) n-1 × 2n-2, (- 1) n + 1 × 2n, ∵ the three adjacent sums are 1224, ∵ n × 2N-1 + (- 1) n-1 × 2n-2 + (- 1) n + 1 × 2n = 1224, ∵ - 1) n-1 × 2n-2 = 408, ∵ n-1 is even, ∵ n must be odd. ∵ 2n-2 = 408, ∵ n does not exist There are three adjacent sums of 1224, which is wrong

Square of a + square of 2A (a + b) + (a + b) to the fourth power
Factorization is complete

a^2+2a（a+b）^2+（a+b）^4
=[a+(a+b)^2]^2

Solving linear equation with one variable in 3.3 of PEP seventh grade volume I (2) -- removing bracket and denominator to expand the thinking of solving 15 problems
A goes from a to B by bike, B goes from B to a by bike, both of them move forward at a constant speed. It is known that they start at 8 am at the same time. By 10 am, they are 36 km apart. By 12 noon, they are 36 km apart. Find the distance between a and B
(x-36)/(10-8)=(36+36)/(12-10)
x=108
I want to talk on the blackboard,

After departure, the two people walked opposite each other. From "to 10 am, they were 36 kilometers apart. To 12 noon, they were 36 kilometers apart." it can be seen that at 10 am, they had not met yet, but at 12 noon, they had "passed each other" and were walking backwards, so they walked a total of (36 + 36) kilometers in the two hours from 10 am to 12 pm, The sum of the two speed can be calculated as (36 + 36) / (12-10) km / h. from 8 am to 10 am, if a and B are x km apart, we can know that they have walked (x-36) km, and the sum of the two speed can also be calculated as (x-36) / (10-8) km / h, B the distance between the two places is 108 kilometers

First row: 3 9 6 4 5 second row: 18 47 31 third row: 6 25 17 15 what is the number of question marks

First row: 3 9 6 4 5
Second row: 18 47 31 17 49
Third row: 6 25 17 15 - 9
The sum of all the numbers in each column is 9 times of the first number in this column;
The sum of all the numbers in each row is nine times the first number in this row

The absolute value is not less than 2, and the product of all negative integers of Xiaoyu 5 is

Negative integers with absolute values less than 5 include: - 1, - 2, - 3, - 4
Negative integers with absolute value not less than 2 include: - 2, - 3, - 4, - 5
All negative numbers whose absolute value is not less than 2 but less than 5, i.e. - 2 ≤ x

Science and technology books account for 40% of the total books in the school library, and story books account for 30% of the total books. There are 1200 more science and technology books than story books?