31-32+33-34+35-36+................-2014+2015 =?
K
Khách
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2 tháng 10 2016
(31+39)+(32+38)+(33+37)+(34+36)+(30+31+35)=70+70+70+70+96=376
TL
1
3 tháng 3 2019
ta có: \(\frac{31+32+35}{34}=\frac{31}{34}+\frac{32}{34}+\frac{35}{34}.\)
mà \(\frac{31}{32}>\frac{31}{34};\frac{32}{33}>\frac{32}{34}\)
\(\Rightarrow\frac{31}{32}+\frac{32}{33}+\frac{35}{34}>\frac{31}{34}+\frac{32}{34}+\frac{35}{34}=\frac{31+32+35}{34}\)
LN
1
KV
24 tháng 3 2022
Ta có: \(\dfrac{1}{4}=\dfrac{10}{40}=\dfrac{1}{40}+\dfrac{1}{40}+\dfrac{1}{40}+\dfrac{1}{40}+\dfrac{1}{40}+\dfrac{1}{40}+\dfrac{1}{40}+\dfrac{1}{40}+\dfrac{1}{40}+\dfrac{1}{40}\)
Mà \(\dfrac{1}{31}>\dfrac{1}{40}\)
\(\dfrac{1}{32}>\dfrac{1}{40}\)
\(\dfrac{1}{33}>\dfrac{1}{40}\)
\(\dfrac{1}{34}>\dfrac{1}{40}\)
\(\dfrac{1}{35}>\dfrac{1}{40}\)
\(\dfrac{1}{36}>\dfrac{1}{40}\)
\(\dfrac{1}{37}>\dfrac{1}{40}\)
\(\dfrac{1}{38}>\dfrac{1}{40}\)
\(\dfrac{1}{39}>\dfrac{1}{40}\)
\(\Rightarrow\) \(\dfrac{1}{31}+\dfrac{1}{32}+\dfrac{1}{33}+...+\dfrac{1}{39}+\dfrac{1}{40}>\dfrac{10}{40}=\dfrac{1}{4}\)
Vậy \(S>\dfrac{1}{4}\)
9 tháng 6 2017
Ta có :
x = 31 + 32 - 33 + 34 - 35 + 36 - 37 + 38 - 39 + 40
x = 31 - 32 + 33 - 34 + 35 - 36 + 37 - 38 + 39 + 40
x = 31 - ( 33 - 32 ) - ( 35 - 34 ) - ( 37 - 36 ) - ( 39 - 38 ) + 40
x = 31 - 1 - 1 - 1 - 1 + 40
x = 67
Vậy giá trị của biểu thức trên là 67
OS
1
TC
2
6 tháng 11 2015
Bài 1: ĐS: 34
Bài 2: ĐS: 15
Đúng thì nhớ link ĐÚNG cho mình nha!
3 tháng 5 2018
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30+31+32+33+34+35+36+37
=(1+37)x37:2
=703
9 tháng 7 2023
31. How old is she?
32. How is she?
33. My children go to school by bike.
34. We go to the supermarket to buy some food.
35. Mr. Hien goes on business to Hanoi every month.
36. Ha likes coffee very much, but I don't like it.
37. She likes tea, but she doesn't like coffee.
38. I love cats, but I don't love dogs.
39. Every day, I go to school on foot.
40. Who are you waiting for, Nam?
- No, I am waiting for Mr. Hai.
41. My sister gets dressed and brushes her teeth herself at 6.30 every day.
42. Mrs. Smith doesn't live in downtown. She rents an apartment in the suburb.
43. How do your children go to school every day?
44. It's 9 o'clock in the morning. Lien is in her room. She is listening to music
45. We are playing soccer in the yard now.
46. My father goes to work by bike. Sometimes he walks.
47. Do you live near a market? Is it noisy?
48. Now I am doing the cooking while Hoa is listening to music.
49. At the moment, Nam and his friends are going shopping at the mall.
50. In the autumn, I rarely go sailing and rarely go to school.
51. I am writing a letter to my friend now.
52. At 12 a.m every day, I have lunch and go to bed.
53. On Monday, I have math and Art.
54. On Friday, she has English.
55. At the moment, I am eating an orange, and my sisters are playing tennis.
56. Is it her bag? - No, it is not hers
57. What time do your children go to school?
58. He lives in HCM City.
59. What time does your brother usually get up?
60. My house is in the city and it is small.
61. Every morning, we have breakfast at 7.00 am.
#Salem
tổng trên có số hạng tử là (2015-31):1+1=1985(hạng tử)
tổng trên =-1-1-1-...-1+2015=-1984+2015=31
tích đúng cho mk nhé