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1 Calculation （1+1／11+1／13+1／17）（1／11+1／13+1／17+1／19）-（1+1／11+1／13+1／17+1／19）（1／11+1／13+1／17） 2 Calculation （1／2+1／3+.+1／2005）（1+1／2+1／3+.+1／2004）-（1+1／2+...+1／2005）（1／2+1／3+...+1／2004）
Question 1: first of all, take apart the formula after the minus sign: (1 + 1 / 11 + 1 / 13 + 1 / 17) (1 / 11 + 1 / 13 + 1 / 17 + 1 / 19) - (1 + 1 / 11 + 1 / 13 + 1 / 17 + 1 / 19) (1 / 11 + 1 / 13 + 1 / 17) = (1 + 1 / 11 + 1 / 13 + 1 / 17) (1 / 11 + 1 / 13 + 1 / 17 + 1 / 19) - (1 + 1 / 11 + 1 / 17) = (1 + 1 / 11 + 1 / 13 + 1 / 17) (1 / 11 + 1 / 11 + 1 / 19)
If there are three commemorative coins on the table, all of them face up, now let's play a game: flip two of them at the same time each time, ask: can you flip them several times to make all the three commemorative coins face up?
Write a + 1 on the front and a - 1 on the back of each coin. Each flip is equivalent to multiplying the number on the upper side by - 1
Study the product of three numbers on the upward side of three gold coins, and record this product as S
When the three gold coins are all face up, s = (+ 1) * (+ 1) * (+ 1) = + 1
If you flip two gold coins at the same time each time, try several times to see if you can make the reverse sides of the three gold coins all up, that is, s = (- 1) * (- 1) * (- 1) = - 1
Why not?
If there are six gold coins and three of them are flipped each time, can we make the obverse side all up instead of the reverse side all up?
Don't be so abstruse, say it in understandable language,
First of all, it's a good idea to turn it into a mathematical problem. Second, the answer is very simple. Because three coins turn two at a time, three can't be divided by two. So when three coins are positive at the same time, it's impossible to turn two at a time to turn three coins into negative at the same time
Here is a balance, a ruler and a pair of scissors. Please find a way to measure the length of a roll of thin copper wire. Write down the experimental steps and calculation formula
Let the total length and total mass be l, M. first measure the mass of copper wire, i.e. M. cut a section of copper wire with scissors, weigh it as M 'with balance, and measure the length as l' with ruler, then l / M = L '/ M', so l = (L '/ M') * M. of course, different L 'can be taken, and the average value can be taken for multiple measurements~
Answers to the exercise book of Chinese Lesson 11 of Jiangsu Education Press
1、 1. To read a good book is to talk with a noble person. Reading a good book is as if the person is reasoning with you. 2. Biographies of celebrities; achievements of people engaged in intellectual activities. 3. Autobiography of Lao She, autobiography of Ba Jin, autobiography of Lu
The greatest common factor of two numbers is 1, and the least common multiple is 24. What are the two numbers?
3,8 or 1,24
The ratio of X to 13 is 4:3, and the quotient of X divided by 4.2 is 35
The ratio of X to 13 is 4:3
x=52/3
The quotient of X divided by 4.2 is 35
x=147
(1) any rational number less than one is greater than its square; (2) if a > b
In the following statements, the correct ones are ()
① Any rational number less than one is greater than its square; ② if a > b, then a & # 178; > b & # 178;; ③ (M + 1) &# 178; is non negative; ④
The cube of a rational number greater than 0 and less than 1 must not be greater than the original number; 5. The cube of a rational number greater than - 1 and less than 0 must be greater than the original number
A. 1 B. 2 C. 3 d. more than 3
① Wrong, the square of 0 equals 0
② Wrong, 0 ＞ - 1, but (- 1) &# 178; > 0 &# 178;
③ Right
④ Right
⑤ Right
So choose C
In particular, it is emphasized that (4) is right, although the cube of rational numbers greater than 0 and less than 1 must be less than the original number, but less than the one that does not violate the title is not greater than
Fill in the blanks. 1 / 2, 2 / 6, 4 / 18, 8 / 72____ ,____ .
1 in 2, 2 in 6, 4 in 18, 82 in 72, 16 in 88, 32 in 440
The numerator is two times of the preceding numerator, and the denominator is three, three, four, four, five times of the preceding denominator (according to this rule)
If (x + y) ^ 2 = 7, (X-Y) ^ 2 = 3, then the value of XY is
(x+y)^2=7
x²+2xy+y²=7.①
(x-y)^2=3
x²-2xy+y²=3.②
①-②
4xy=4
xy=1
If you don't know, ask again
How to prove the reflection of light with the law of refraction?
Reflection occurs when you set it on a plane. According to the refraction law N1 * sin α 1 = N2 * sin α 2, reflection: N1 = N2, α 1, α 2 are either equal or complementary. If they are equal, it means that a straight line passes through the object, abandons and complements. Then the reflection angle and incidence angle are equal
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