a, A=1.7+7.13+13.19+19.25+.....+9.97
b, B= 2^2+3^2+4^2+...........+80^2
c, C=1.99+2.98+3.97+.......+99.1
giúp mình đc ko
mình đang cần gấp
Những câu hỏi liên quan
1.99^2+2.98^2+3.97^2+....+98.2^2+99.1^2 Giúp mình vớiiiii
1/1.7+1/7.13+1/13.19+1/19.25+1/25.31+1 / 31.37 = ?
1/7+1/91+1/247+1/475+1/775+1/1147=? (1)
ta có: (1) <=>: 1/(1.7)+1/(7.13)+1/(13.19)+1/(19.25)+1/(25.31)+1/(31.37)
=1/6.(1-1/7+1/7-1/13+1/13-1/19+1/19-1/25+1/25-1/31+1/31-1/37)
=1/6.(1-1/37)=6/37
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Tính :
A = 1.2+2.3+3.4+...+99.100
B = 1.3+2.4+3.5+...+99.101
C = 1.3+3.5+5.7+...+97.99+99.101
D = 1.4+2.5+3.6+...+99.102
E = 12+22+32+...+992+1002
F = 1.99+2.98+3.97+...+98.2+99.1
Mình cần gấp lắm ! Ai làm được cho mình trước trình bày đầy đủ mình kick cho
Xem thêm câu trả lời
Tính:
A =1^2+2^2+3^2+...+97^2+98^2
B =1.99+2.98+3.97+...+98.2+99.1
=1.99+2.(99-1)+3.(99-2)+...+98.(99-97)+99(99-98)
=99.(1+2+3+4+...+98+99)-(2+2.3+3.4+...+97.98+98.99)
=99.(1+99).99/2-98.99.100/3
=99.50.99-98.33.100
=490050-323400
=166650
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1/1.7+1/7.13+1/13.19+......+1/61.67
1/1.2.3+1/2.3.4+1/3.4.5+.......+1/8.9.10
1/1+2 + 1/1+2+3 + 1/1+2+3+4 +.......+ 1/1+2+3+....+99
CẦN GẤP
\(\frac{1}{1.7}+\frac{1}{7.13}+\frac{1}{13.19}+...+\frac{1}{61.67}\)
=6.\(\left(\frac{1}{1.7}+\frac{1}{7.13}+...+\frac{1}{61.67}\right)\):6
=\((\frac{6}{1.7}+\frac{6}{7.13}+...+\frac{6}{61.67}):6\)
=\(\left(1-\frac{1}{7}+\frac{1}{7}+\frac{1}{13}+...+\frac{1}{61}+\frac{1}{67}\right):6\)
=\(\left(1-\frac{1}{67}\right):6\)
=\(\frac{66}{67}:6=\frac{66}{67}.\frac{1}{6}=\frac{11}{67}\)
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Bài tập:
1. Tính A12+42+72+...+1002
2. Tính B1.32+3.52+5.72+...+97.992
3. Tính A1.99+2.98+3.97+...+49.51+50.50
4. Tính B1.3+5.7+9.11+...+97.101
5. Tính C1.3.5-3.5.7+5.7.9-7.9.11+...-97.99.101
6. Tính D1.99+3.97+5.95+...+49.51
7. Tính E1.33+3.53+5.73+...+49.513
8. Tính F1.992+2.982+3.972+...+49.512
Ai giúp mk với mk tick cho
Đọc tiếp
Bài tập:
1. Tính A=12+42+72+...+1002
2. Tính B=1.32+3.52+5.72+...+97.992
3. Tính A=1.99+2.98+3.97+...+49.51+50.50
4. Tính B=1.3+5.7+9.11+...+97.101
5. Tính C=1.3.5-3.5.7+5.7.9-7.9.11+...-97.99.101
6. Tính D=1.99+3.97+5.95+...+49.51
7. Tính E=1.33+3.53+5.73+...+49.513
8. Tính F=1.992+2.982+3.972+...+49.512
Ai giúp mk với mk tick cho
Tính:
a) C= 2/1.7+ 2/7.13+2/13.19+...+2/1013.1019
b) D= 7/1.9+7/9.17+7/17.25+...+7/2011.2019
a/\(C=\dfrac{2}{1.7}+\dfrac{2}{7.13}+\dfrac{2}{13.19}+...+\dfrac{2}{1013.1019}\)
\(=\dfrac{1}{3}\left(\dfrac{6}{1.7}+\dfrac{6}{7.13}+\dfrac{6}{13.19}+...+\dfrac{6}{1013.1019}\right)\)
\(=\dfrac{1}{3}\left(1-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{19}+...+\dfrac{1}{1013}-\dfrac{1}{1019}\right)\)
\(=\dfrac{1}{3}\left(1-\dfrac{1}{1019}\right)\)
\(=\dfrac{1}{3}\cdot\dfrac{1018}{1019}\)
\(=\dfrac{1018}{3057}\)
b/\(D=\dfrac{7}{1.9}+\dfrac{7}{9.17}+\dfrac{7}{17.25}+...+\dfrac{7}{2011.2019}\)
\(=\dfrac{7}{8}\left(\dfrac{8}{1.9}+\dfrac{8}{9.17}+\dfrac{8}{17.25}+...+\dfrac{8}{2011.2019}\right)\)
\(=\dfrac{7}{8}\left(1-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{17}+\dfrac{1}{17}-\dfrac{1}{25}+...+\dfrac{1}{2011}-\dfrac{1}{2019}\right)\)
\(=\dfrac{7}{8}\left(1-\dfrac{1}{2019}\right)\)
\(=\dfrac{7}{8}\cdot\dfrac{2018}{2019}\)
\(=\dfrac{7063}{8076}\)
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a) Ta có :
\(C=\dfrac{2}{1.7}+\dfrac{2}{7.13}+\dfrac{2}{13.19}+...+\dfrac{2}{1013.1019}\)
\(\Rightarrow C=\dfrac{1}{3}.\left(\dfrac{6}{1.7}+\dfrac{6}{7.13}+\dfrac{6}{13.19}+...+\dfrac{6}{1013.1019}\right)\)
\(\Rightarrow C=\dfrac{1}{3}.\left(\dfrac{1}{1}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{19}+...+\dfrac{1}{1013}-\dfrac{1}{1019}\right)\)
\(\Rightarrow C=\dfrac{1}{3}.\left(\dfrac{1}{1}-\dfrac{1}{1019}\right)\)
\(\Rightarrow C=\dfrac{1}{3}.\dfrac{1018}{1019}\)
\(\Rightarrow C=\dfrac{1018}{3057}\)
b) Ta có:
\(D=\dfrac{7}{1.9}+\dfrac{7}{9.17}+\dfrac{7}{17.25}+...+\dfrac{7}{2011.2019}\)
\(\Rightarrow D=\dfrac{7}{8}.\left(\dfrac{8}{1.9}+\dfrac{8}{9.17}+\dfrac{8}{17.25}+...+\dfrac{8}{2011.2019}\right)\)
\(\Rightarrow D=\dfrac{7}{8}.\left(\dfrac{1}{1}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{17}+\dfrac{1}{17}-\dfrac{1}{25}+...+\dfrac{1}{2011}-\dfrac{1}{2019}\right)\)
\(\Rightarrow D=\dfrac{7}{8}.\left(\dfrac{1}{1}-\dfrac{1}{2019}\right)\)
\(\Rightarrow D=\dfrac{7}{8}.\dfrac{2018}{2019}\)
\(\Rightarrow D=\dfrac{7063}{8076}\)
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Tìm giá trị của biểu thức
A=1+2-3-4+5+6-7-8+...(2018 số hạng)
B=1.99+2.98+3.97+...+98.2+99.1
A= (2018+1) x 2018 : 2 = 2037171
B= ko biết làm
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Tính giá trị biểu thức
A=1+2-3-4+5+6-7-8+...(2018 số hạng)
B=1.99+2.98+3.97+...+99.1+98.2
a bn tự lm nha mk lm đỡ bn phần b
b=1.99+1.98+3.97+...+98.2+99.1
= 1.99+2.(99-1)+3.(99-2)+...+98.(99-97)+99.(99-98)
= 1.99+2.99-1.2+3.99-2.3+...98.99-97.98+99.99-99.98
=(1.99+2.99+3.99+...+98.99+99.99)-(1.2+2.3+...+98.99)
=99.(1+2+3+...+98+99)-(1.2+2.3+...+98.99)
=99.4950-(1.2+2.3+...+98.99)
=490050-(1.2+2.3+...+98.99)
b=1.2+2.3+...+98.99
3b=1.2.3+2.3.3+...+98.99.3
3b=1.2.3+2.3.(4-1)+...+98.99.(100-97)
3b=1.2.3+2.3.4+2.3.1+...+98.99.100+98.00.97
3b=490050-(98.99.100):3
b=490050-323400
b=166650
tk mk nha
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=1.99+2.(99-1)+3.(99-2)+...+98.(99-97)+99(99-98)
=99.(1+2+3+4+...+98+99)-(2+2.3+3.4+...+97.98+98.99)
=99.(1+99).99/2-98.99.100/3
=99.50.99-98.33.100
=490050-323400
=166650
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