There are some books on Xiaoming's bookshelf. The number of books ranges from 100 to 150. Among them, 15 are story books, 17 are science and technology books, and most of them are on the bookshelf______ This is a book

There are some books on Xiaoming's bookshelf. The number of books ranges from 100 to 150. Among them, 15 are story books, 17 are science and technology books, and most of them are on the bookshelf______ This is a book

According to the meaning of the title, the number of books can be divided not only by 5, but also by 7 10, 4 × 35 = 140. A: there are 140 books on the shelf at most

The original number of science and technology books in the school library accounts for 25% of the number of story books. Now we have bought another 60 science and technology books. At this time, the ratio of science and technology books to story books is 4:7. There were () science and technology books in the library
A. 350B. 140C. 200D. 80

60 (47-25) = 60 (635) = 350 (copies) 350 × 25 = 140 (copies) answer: 140 original scientific and technological books

How much is 2 plus 52.8 times 5 minus 3.9443 divided by 0.5 minus ten times this number?

It's 520.1314. It's very romantic. It's in my book~

Given that the solutions of the equations ax − by = 42x + 3Y = 4 and ax + by = 24x − 3Y = 2 are the same, then a + B=______ ．

By solving the equations 2x + 3Y = 44x − 3Y = 2, we can get x = 1y = 23. By substituting the values of X and Y into ax by = 4, ax + by = 2, we can get the equations a − 23B = 4A + 23B = 2, we can get a = 3B = − 1.5, a + B = 3-1.5 = 1.5

What is sin ^ 2, what is sin ^ 260 ° and what is cos ^ 43 / 2

Sin ^ 2 is the square of SiNx
Sin260 equals sin80
The last one didn't quite understand

To calculate the determinant, the first line is 4124, the second line is 1202, the third line is 10520, and the fourth line is 0117

The first row is 4124, the second row is 1202, the third row is 10520, the fourth row is 0117, the fourth column subtracts the second column, and the second column subtracts two times of the first column to get: the first row is 4-723, the second row is 1000, the third row is 10-152-5, and the fourth row is 0116

Five eighths divided by 79.23 and one sixteenth divided by 79.23

(5/8+1/1600)/79.23=0.00789631

When x tends to 0, we find the limit of e ^ (1 / x)
Is the limit zero when it tends to zero negative and infinite when it tends to 0 +?

When x tends to 0 from less than 0, 1 / X tends to negative infinity and e ^ (1 / x) tends to 0
When x tends to 0 from greater than 0, 1 / X tends to positive infinity, and e ^ (1 / x) tends to positive infinity
So it doesn't exist,

Simple calculation, 5 / 12 * 2 / 5 + 7 / 12 * 2 / 5

2/5（5/12+7/12）=2/5

Factorization a ^ 2B ^ 2-C ^ 2

a²b²-c²
=(ab-c)(ab+c)