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\(S=\frac{5^2}{1.6}+\frac{5^2}{6.11}+...+\frac{5^2}{26.31}\)
\(S=5.\left(\frac{5}{1.6}+\frac{5}{6.11}+...+\frac{5}{26.31}\right)\)
\(S=5.\left(1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+...+\frac{1}{26}-\frac{1}{31}\right)\)
\(S=5.\left(1-\frac{1}{31}\right)\)
\(S=5.\frac{30}{31}\)
\(S=\frac{150}{31}\)
Câu L bạn thiếu số\(\frac{1}{475}\)
\(L=\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+\frac{1}{475}+\frac{1}{775}+\frac{1}{1147}\)
\(L=\frac{1}{1.7}+\frac{1}{7.13}+\frac{1}{13.19}+\frac{1}{19.25}+\frac{1}{25.31}+\frac{1}{31.37}\)
\(L=\frac{1}{6}.\left(\frac{6}{1.7}+\frac{6}{7.13}+\frac{6}{13.19}+\frac{6}{19.25}+\frac{6}{25.31}+\frac{6}{31.37}\right)\)
\(L=\frac{1}{6}.\left(1-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+\frac{1}{13}-\frac{1}{19}+\frac{1}{19}-\frac{1}{25}+\frac{1}{25}-\frac{1}{31}+\frac{1}{31}-\frac{1}{37}\right)\)
\(L=\frac{1}{6}.\left(1-\frac{1}{37}\right)\)
\(L=\frac{1}{6}.\frac{36}{37}\)
\(L=\frac{6}{37}\)
\(S=\frac{5^2}{1.6}+\frac{5^2}{6.11}+...+\frac{5^2}{26.31}\)
\(=5\left[\left(1-\frac{1}{6}\right)+\left(\frac{1}{6}-\frac{1}{11}\right)+...+\left(\frac{1}{26}-\frac{1}{31}\right)\right]\)
\(=5\left[1-\frac{1}{31}\right]\)
\(=5.\frac{30}{31}=\frac{150}{31}\)
\(L=\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+\frac{1}{775}+\frac{1}{1147}\)
\(L.6=\frac{6}{1.7}+\frac{6}{7.13}+\frac{6}{13.19}+\frac{6}{19.25}+\frac{6}{25.31}\)
\(L.6=\left(1-\frac{1}{7}\right)+\left(\frac{1}{7}-\frac{1}{13}\right)+\left(\frac{1}{13}-\frac{1}{19}\right)+\left(\frac{1}{19}-\frac{1}{25}\right)+\left(\frac{1}{25}-\frac{1}{31}\right)\)
\(L.6=1-\frac{1}{31}\)
\(L.6=\frac{31}{31}-\frac{1}{31}\)
\(L.6=\frac{25}{31}\)
\(L=\frac{30}{31}:6\)
\(L=\frac{30}{31}.\frac{1}{6}\)
\(L=\frac{30}{186}\)
1 There is a few water in the bottle
=> There is a little water in the bottle
2 The story is between we house and the movie theater
=> The story is between our house and the movie theater
3 Last summer my parents buyed me a lot of different gifts
=> Last summer my parents bought me a lot of different gifts
1. few water => little water
2. we house => our house
3. buyed => bought
HỌC TỐT ^_^
để 3n+4/n-1 là số nguyên
=>3n+4 chia hết cho n-1
ta có: 3n+4=3.(n-1)+7 chia hết cho n-1
mà 3.(n-1) chia hết cho n-1
=>7 chia hết cho n-1
=>n-1 thuộc Ư(7)={-7;-1;1;7}
ta có bảng sau:
background Layer 1vậy n thuộc {-6;0;2;8}
để 3n+4/n-1 là số nguyên
=>3n+4 chia hết cho n-1
ta có: 3n+4=3.(n-1)+7 chia hết cho n-1
mà 3.(n-1) chia hết cho n-1
=>7 chia hết cho n-1
=>n-1 thuộc Ư(7)={-7;-1;1;7}
ta có bảng sau:
| n-1 | -7 | -1 | 1 | 7 |
| n | -6 | 0 | 2 | 8 |
vậy n thuộc {-6;0;2;8}
\(A=\frac{2}{1.3}+\frac{2}{3.5}+...+\frac{2}{48.50}\)
\(=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{48}-\frac{1}{50}\)
\(=1-\frac{1}{50}\)
\(=\frac{50}{50}-\frac{1}{50}\)
\(=\frac{49}{50}\)
Ta có:\(\frac{49}{50}\)và\(\frac{3}{2}\)
Vì\(\frac{49}{50}< 1;\frac{3}{2}>1\)
\(\Rightarrow\frac{49}{50}< \frac{3}{2}\)
Điền các từ sau vào chỗ chấm thích hợp để hoàn thành đoạn văn :from ,means,in,waste ,possible ,wind,should,green.However,who .
Much of our waste ,especailly waste(1)…………from………………..factories,eletric-powered stations ,the chemical industry and heavy industry ,is very dangerous .Fish die (2) ……………in……………..the lakes,riversand seas;forest tree die,too .Much of this dangerous(3) ……………waste……………..goes into the air and is carried by the(4) ………wind…………………..for great distances .
The Earthis our home.We (5) ……………should……………..take care of it,for ourselves,and for our children and grandchildren .This (6) ………means…………………..we have to keep our environment (7) …………green………………..and clean.The important of this task is pointed out by ecologists-the scientist(8) ………who…………………..study the relations between living things and the environment .(9) ……………However……………..,each of us must do everything (10) ……possible……………………..to keep the land ,air and water clean.
1-The number of time he spends gardening is increasing every day
2-It would be both noed and appreciating if you could finish the work before you leave
3-The suits were hanged in the closet when they were returned from the cleaners
4-A vast quantity of radioactive material is made when a hydfrogen bomb explode
2,could finish=>finished๖²⁴ʱŠїêʉ şαø вóηɠ đá"NCTK"