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T
3
24 tháng 3 2021
Ta có: \(S=\dfrac{4}{1\cdot3}+\dfrac{16}{3\cdot5}+\dfrac{36}{5\cdot7}+...+\dfrac{2500}{49\cdot51}\)
\(=1+\dfrac{1}{1\cdot3}+1+\dfrac{1}{3\cdot5}+1+\dfrac{1}{5\cdot7}+...+1+\dfrac{1}{49\cdot51}\)
\(=25+\dfrac{1}{2}\cdot\left(\dfrac{2}{1\cdot3}+\dfrac{2}{3\cdot5}+\dfrac{2}{5\cdot7}+...+\dfrac{2}{49\cdot51}\right)\)
\(=25+\dfrac{1}{2}\cdot\left(\dfrac{1}{1}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{49}-\dfrac{1}{51}\right)\)
\(=25+\dfrac{1}{2}\left(1-\dfrac{1}{51}\right)\)
\(=25+\dfrac{1}{2}\cdot\dfrac{50}{51}\)
\(=25+\dfrac{25}{51}\)
\(=25\cdot\dfrac{52}{51}=\dfrac{1300}{51}\)
5 tháng 8 2016
ta có 3S=\(3\left(3+3^2+3^3+...+3^{2010}\right)\)
3S=\(3^2+3^3+3^4+3^5+...+3^{2011}\)
2S=3S-S=\(3^2+3^3+3^4+3^5+...+3^{2011}\)-\(-\)\(3+3^2+3^3+...+3^{2010}\)
2S=\(3^{2011}-3\)
=> 2S+3 =3x
=>\(3^{2011}-3+3=3x\)
=>x=\(3^{2010}\)
TT
2
B
25 tháng 12 2022
1 Show me the new hats which you bought last night
2 That is a company which produces diamond rings
3 My best friend who sings folk songs very well can compose songs
4 Zoe bought a new phone which is quite expensive yesterday
5 The man whom you met last week is her father
6 Zoe likes the blue T-shirt which she is wearing
7 Zoe has a sister whose name is Juma
8 The children were attracted by the show in which there were so many famous people
9 Tet is a festival that often happens in late January or early February
10 Jack is the boy who gave my mom a gift
NP
Ngô Phương
Admin
VIP
25 tháng 12 2022
1. Show me the new hats which you bought last night.
2. That is a company which produces diamond rings.
3. My best friend, who sings folk songs very well, can compose a song.
4. Zoe bough a new phone yesterday, which is expensive.
5. The man who you met last week is her father.
6. Zoe like the blue t-shirt which my sister is wearing.
7. Zoe has a sister whose name is Juma.
8. The children were attracted by the show which there were so many famous people.
9. Tet is a festival which often happens in late January or early February.
10. Jack is the boy who gave my mom a gift.
19 tháng 6 2018
gọi số đó là ab
ta có: ab=8x(a+b)
a x 10 + b =8 x a + 8 x b
a x 2=b x 7
vậy : ab =72
NV
19 tháng 6 2018
Gọi số đó là ab
Theo đề bài ta có:
ab = 8( a+ b )
10a + b = 8a + 8b
2a = 7b ( bớt mỗi bên đi 8a + b )
=> a = 7
b = 2
Vậy số cần tìm là 72
CÁC BẠN GIÚP MÌNH NHÉ MÌNH CẢM ƠN
5 tháng 9 2021
Bài 11:
a: \(4x^2-1=\left(2x-1\right)\left(2x+1\right)\)
b: \(25x^2-\dfrac{9}{100}=\left(5x-\dfrac{3}{10}\right)\left(5x+\dfrac{3}{10}\right)\)
c: \(9x^2-\dfrac{1}{4}=\left(3x-\dfrac{1}{2}\right)\left(3x+\dfrac{1}{2}\right)\)
d: \(\left(x-y\right)^2-4=\left(x-y-2\right)\left(x-y+2\right)\)