-(2 * 3) 1 / 2 - (3 * 4) 1 / 2 ·· - (1999 * 2000) 1 / 2

-(2 * 3) 1 / 2 - (3 * 4) 1 / 2 ·· - (1999 * 2000) 1 / 2

-《1/(2*3)+1/(3*4)+1/(4*5)+...1/（n*(n+1)）》=-《(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+.（1/n-1/(n+1)）》=-《1/2-1/(n+1)》=-1999/2000

F (x) = 9 ^ X / (9 ^ x + 3), find f (1 / 2000) + F (2 / 2000) + +f(1999/2000)

∵ f (x) + F (1-x) = 9 ^ X / (9 ^ x + 3) + 9 ^ (1-x) / (9 ^ (1-x) + 3) = (9 + 3 * 9 ^ x + 9 + 3 * 9 ^ (1-x)) / (9 + 9 + 3 * 9 ^ x + 3 * 9 ^ (1-x)) = 1 +f(1000/2000)=999+f(1/2)=999+3/(3+3)=999.5

Given that the lengths of the three sides of a triangle are 4, 5 and 6 respectively, the circumference of the triangle enclosed by its three median lines is______ ．

∵ the lengths of each side of the new triangle are: 4 △ 2 = 2, 5 △ 2 = 2.5, 6 △ 2 = 3, and the circumference of the new triangle is 2 + 2.5 + 3 = 7.5

[(A-1 / 2) squared + (a + 1 / 2) squared] (2a squared-1 / 2)
Please help, qua

（a-1/2)^2=a^2-a+1/4 ;（a+1/2)^2=a^2+a+1/4
[（a-1/2)^2+（a+1/2)^2]*[2a^2-1/2]=][2a^2+1/2]]*[2a^2-1/2]=4a^4-1/4

Crazy guess idiom left a South word, right a horse is what idiom?

Ma Fangnan mountain

Teaching plan of what are the same characteristics of plants

Scientific concept: according to the living environment, plants can be divided into terrestrial plants and aquatic plants. The survival of plants needs water, sunlight, air and nutrition, Each plant has a certain life span. The common characteristics of plants are: growing in a certain environment, all need water, sunlight, air and nutrition, all can grow and develop, all can reproduce, and all have the life process from birth to death. Process and method: using the comparative method to get the understanding of the common characteristics. Emotion, attitude, values: through the understanding of the life span of plants, we can understand the value of life, Teachers: pictures of aquatic plants and terrestrial plants, pictures of plant life; students: comparison record paper of aquatic plants and terrestrial plants, Recall: there are many plants growing around us. We have known big trees, Setaria, water hyacinth and goldfish algae. We also know which terrestrial plants and aquatic plants are recorded in the following record sheet. (group discussion record) terrestrial plants, aquatic plants 2, Thinking: what do plants need to grow normally? Please communicate. Please read "plants need sunshine" in p21__________________________________________ The growth needs of aquatic plants__________________________________________ Can we record the common points of their survival needs with wientu? Student report 2: understand the life of plants. Thinking about: what changes have plants experienced in their life? Please see the picture: the life of sunflower. Can we find out several typical growth stages of sunflower's life? Seeds, germination, seedlings, flowering and fruiting are the typical growth stages of sunflower's life, Can you find out the similarities and differences with sunflower's life? By the way, the main difference is the length of life. Please look at the database: "plant's life is long and short". What do you know? Yes, whether it's a hundred year old tree or a year old herb, they will die. This is the law of nature and the characteristic of life, What are the common characteristics of plants? Thinking: after we have observed and studied plants, we can tell what are the common characteristics of plants. How do we know them? Sorting out: look at the records of wientu in previous lessons, compare the common points, and then sort out the records on paper, All of them have the same basic structural characteristics: root, stem, leaf, flower, fruit and seed. Conclusion: as a living body, plants have many important characteristics, such as common growth requirements, growth and development, reproduction, aging and death, There are also the structural characteristics of adapting to the environment (water hyacinth), etc. (such summary must be based on the development of students, students can sum up a few, count a few, don't force, also can't memorize by rote!)

Given that the value of the algebraic formula - 5x ^ 2 + ax + BX ^ 2 + 2x-5 has nothing to do with the value of X, find the value of a and B. can you explain it to me in detail

-5x²+ax+bx²+2x-5=(b-5)x²+(a+2)x-5
The value of known algebraic formula - 5x ^ 2 + ax + BX ^ 2 + 2x-5 has nothing to do with the value of X
Then B-5 = 0, a + 2 = 0
So a = - 2, B = 5

A rectangular playground is 100 meters long and 2.5 cm long. What's the scale of this picture

100 m = 10000 cm
2.5:10000=1 :4000

Write a fable, fairy tale, write your dream or hope composition more than 300 words

Once upon a time, there was a lovely rabbit in the forest kingdom, named Beibei. She used to be a hygiene rabbit, but now she seems to have changed. Mother rabbit reminded Beibei several times, and she said, "I know, don't bother me!" mother rabbit had to go away angrily. Time went by little, and Beibei rabbit grew up gradually

Known: three consecutive odd numbers, their sum of squares is 251, find these three odd numbers

Let these three odd numbers be n-2, N, N + 2 in turn, where n is a natural number, then n > 2, then according to the problem meaning, we can get the following equation: (n-2) 2 + N2 + (n + 2) 2 = 251, 3N2 = 243, N2 = 81, n = 9 or n = - 9, when n = 9, n-2 = 7, N + 2 = 11; when n = - 9, n-2 = - 11, N + 2 = - 7; answer: these three consecutive odd numbers are 7, 9, 11 or - 7, - 9, - 11