a)2/1x4+2/4x7+2/7x10+...+2/97x100
b)3/1x5+3/5x9+3/9x13+...+3/97x101
giúp mk nốt câu này luôn nha các bạn vì mk đang cần rất rất chi là gấp luôn í!
tính 2/1x5+2/5x9+2/9x13+...+2/93x97+2/97x101 giúp mik với ak mik thi gấp lắm ạ mong mn giúp ạ cảm ơn mn rất rất nhìu ạ
`2/[1xx5]+2/[5xx9]+2/[9xx13]+....+2/[93xx97]+2/[97xx101]`
`=1/2xx(4/[1xx5]+4/[5xx9]+4/[9xx13]+....+4/[93xx97]+4/[97xx101])`
`=1/2xx(1-1/5+1/5-1/9+1/9-1/13+...+1/93-1/97+1/97-1/101)`
`=1/2xx(1-1/101)`
`=1/2xx100/101`
`=50/101`
bn ghi rõ đc ko ạ mik ko hiểu lắm c.ơn bn
A=3^2/1x4+3^2/4x7+3^2/7x10+...+3^2/97x100
\(A=3\times\left(\frac{3}{1\times4}+\frac{3}{4\times7}+\frac{3}{7\times10}+...+\frac{3}{97\times100}\right)\)
\(A=3\times\left(\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{97}-\frac{1}{100}\right)\)
\(A=3\times\left(1-\frac{1}{100}\right)\)
\(A=3\times\frac{99}{100}\)
\(A=\frac{297}{100}\)
\(A=\frac{3^2}{1.4}+\frac{3^2}{4.7}+\frac{3^2}{7.10}+......+\frac{3^2}{97.100}\)
\(A=3.\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+....+\frac{3}{97.100}\right)\)
Đặt \(S=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{97.100}\)
Ta có: \(S=\frac{3}{3}.\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+.....+\frac{3}{97.100}\right)\)
\(S=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+.....+\frac{1}{97}-\frac{1}{100}\)
\(S=1-\frac{1}{100}=\frac{99}{100}\)
\(\Rightarrow A=3.S=3.\frac{99}{100}=\frac{297}{100}\)
Tính
1/1x4+1/4x7+...+1/61x64
3/1x5+3/5x9+...+3/97x101
4/1x3x5+4/3x5x7+...+4/47x49x51
tinh tong 99x100+100x101+............+199x200
1x3+3x5+5x7+.............+99x101
21x23+23x25+25x27+.............+111x113
1x4+4x7+7x10+.............+100x103
1x5+5x9+9x13+ .......................+101x105
a) C=1/9x10+1/18x13+1/26x17+.......+1/802x405
b)D=2/4x7-3/5x9+2/7x10-3/9x13+......+2/302x304+3/401x405
11/1x4+11/4x7+11/7x10+...11/100x103
1/5x9+1/9x13+1/13x17+...+1/2450
mình cần gấp nhé
\(\frac{11}{1.4}+\frac{11}{4.7}+...+\frac{11}{100.103}\)
\(=\frac{11}{3}\left(\frac{3}{1.4}+\frac{3}{4.7}+...+\frac{3}{100.103}\right)\)
\(=\frac{11}{3}\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{100}-\frac{1}{101}\right)\)
\(=\frac{11}{3}\left(1-\frac{1}{103}\right)\)
Tự tính
\(\frac{11}{1.4}+\frac{11}{4.7}+...+\frac{11}{100.103}\)
= \(\frac{11}{3}.\left(\frac{3}{1.4}+\frac{3}{4.7}+...+\frac{3}{100.103}\right)\)
= \(\frac{11}{3}.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{100}-\frac{1}{103}\right)\)
= \(\frac{11}{3}.\left(1-\frac{1}{103}\right)\)
= \(\frac{11}{3}.\frac{102}{103}\)
= \(\frac{374}{103}\)
cho A = 2 + 2^3 + 2^5 + 2^7 + ... + 2^2013 . Tìm số dư khi chia A cho 5
các bạn giải gấp giúp mk nhé , mk đang rất cần nó . các bạn giải luôn cái chi tiết cho mk với .
bạn nào giải đúng mk cho 1 tick nhé , cố lên
Bài 3 :
D = \(\frac{2}{1x4}+\frac{2}{4x7}+\frac{2}{7x10}+...+\frac{2}{97x100}\)
\(D=\frac{2}{1\cdot4}+\frac{2}{4\cdot7}+\frac{2}{7\cdot10}+...+\frac{2}{97\cdot100}\)
\(D=\frac{2}{3}\left(\frac{3}{1\cdot4}+\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+...+\frac{3}{97\cdot100}\right)\)
\(D=\frac{2}{3}\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{97}-\frac{1}{100}\right)\)
\(D=\frac{2}{3}\left(1-\frac{1}{100}\right)\)
\(D=\frac{2}{3}\cdot\frac{99}{100}=\frac{33}{50}\)
Tính nhanh
A=3²/1x4+3² /4x7+3²/7x10+3²/11x12+3²/13x16+. .... +3²/97x100
Giúp mình với nhé