4 out of 5 * 7 out of 9 * 5 out of 8 = simple calculation

4 out of 5 * 7 out of 9 * 5 out of 8 = simple calculation

4/5*7/9*5/8=（4/5*5/8)*7/9=1/2*7/9=7/18

A1, A2, A3... A2008 are all positive numbers
A1, A2, A3 ··· A2008 are all positive numbers. M = (a1 + A2 + a3 + ··· a2007) (A2 + a3 + ··· A2008) n = (a1 + A2 + a3 + ···· + A2008) (A2 + a3 + ··· a2007) compare the size of M n

It's wrong. It's changed back
two thousand and seven
two thousand and eight
2007+1
2008-1
M4030056
N4030056
M=N
(a1 + A2 + a3 + ··· a2007) is set to X
(A2 + a3 + ··· A2008) is set to y
(a1 + A2 + a3 + ·· + A2008) is x + 1
(A2 + a3 + ·· a2007) is Y-1
Let's assume that
X is 2007
Y is 2008
that
X + 1 is 2007 + 1 = 2008
Y-1 is 2008-1 = 2007
Two multipliers are the same, the result is naturally the same

Choose three numbers from 2, 6, 7 and 5 to form a three digit number, making it a multiple of 3. What are these numbers?

Because it's a multiple of three
So three numbers add up to a multiple of three
A: 26727667262772662 and 5675766576756765
A total of 12 numbers
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It is proved that a is an M * n matrix whose rank is R. it is proved that there are invertible matrices P and Q such that the last M-R row of PA and the last N-R column of AQ are all 0
…… Always feel linear algebra can't grasp the clue Now I'm going to study the chapter of matrix. I'm going to work hard on this kind of proof Do you have some kind advice

A is an M * n matrix whose rank is r, so a must be able to be changed into the following form through elementary transformation: 100... 001... 001... 0... 000... 0 means that there is a unit matrix of order r in the upper left corner, and the other elements are all 0. We know that to do an elementary row transformation is to multiply a matrix left by an inverse matrix and do an elementary transformation

For a six digit number, the leftmost number is 1. If the number 1 is moved to the right, the new number is three times of the original number, and how much is the original number

Let the original six digits be 100000 + X
So now it's 10x + 1
So (10x + 1) = 3 * (100000 + x)
x=42857
So the original number is 142857

Two matrices are equivalent, and their rank is the same
If a becomes B after a primary row transformation, then R (a) is less than or equal to R (b)? Why not?

If you think that row a is transformed into B, then the determinant of B will be simpler (it's easier to understand that the determinant value is zero), that is, the rank of B will be larger
That is, R (a) is less than or equal to R (b)
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Ten years of ziyao from Ziba

7 times of X divided by 9 quotient and 7 equations

l2181215 ,
（7X－7）÷9＝7
7X－7＝63
7X＝70
X＝10

8. Approximate and significant numbers
Please judge the correctness of the following questions,
1. The accuracy of approximation 25.0 is the same as that of approximation 25
2. The accuracy of approximate 40 million is the same as that of approximate 40 million
The approximate number is 6.6 million, which is accurate to 10000 bits. There are three significant numbers
4. The approximate numbers 6.40 and 6.4 are equal
5. The quadratic approximation of 3.7x10 is the same as that of 370

1. Wrong. The former is accurate to the tenth place (one place after the decimal point), and the latter to the single digit
2. Wrong. 40 million to tens of thousands, 40 million to tens of thousands
3. Yes
4. Wrong. Although the values are equal, the range and accuracy are different
5. Wrong. 3.7x10 ^ 2 to ten, 370 to one
Related concepts: significant number: refers to the number from the first non-zero number on the left to the end of the number
For example: 3 has one significant number, 0.0003 has one significant number, 0.1500 has four significant numbers, and 1.9 * 10 ^ 3 has two significant numbers (don't be confused by 10 ^ 3, just look at the significant number of 1.9, 10 ^ n is regarded as a unit)
Precision: the unit of the number at the end of a number. For example, 9800.8 is accurate to ten places (also known as one place after the decimal point), 800000 is accurate to ten thousand places, and 9 * 10 ^ 5 is accurate to ten thousand places (a total of nine numbers, 10 ^ n is regarded as a unit, and tens of thousands is a concept)

Xiao Ming read a story book. On the first day, he read 10% of the total pages. On the second day, he read the remaining 20%. On the second day, what percentage of the total pages?

28%

If the set a = {2A square + 5a, 3}, what is the value range of real number a

Not equal to 0.5 and not equal to - 3