1. So sánh không qua quy đồng:
A= -7/102005 + (-15/102006)
B= -15/102005 + (-7/102006)
2. Tính
a. A= -1/20 + (-1/30) + (-1/42) + (-1/56) + (-1/72) + (1/90)
b. B= 5/2.1 + 4/1.11 + 3/11.2 + 1/2.15 + 13/15.4
Những câu hỏi liên quan
không quy đồng hãy tính hợp lý:
A= -1:20+ -1:30+ -1:42+ -1:56+ -1:72+ -1:90
B = 5:2.1+4:1.11+2:11.2+3:2.15+1:2.15+13:15.4
\(A=-\left(\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\right)\)
\(A=-\left(\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{9}-\frac{1}{10}\right)\)
\(A=-\left(\frac{1}{4}-\frac{1}{10}\right)=\frac{-3}{20}\)
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Bài 1 : Không quy đồng hãy tính hợp lý các tổng sau :
a, A = -1/20+-1/30 + -1/42 + -1/56 + -1/72 + -1/90
b, B = 5/2.1 +4/1.11 + 3/11.2 + 1/ 2.15 + 13/15.4
A = - (1/4.5 + 1/5.6 + 1/6.7 + 1/7.8 + 1/8.9 +1/9.10)
A = -( 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + 1/7 - 1/8 + 1/8 - 1/9 + 1/9 - 1/10)
A = -( 1/4 - 1/10)
A = -3/20
B = 7(5/2.7 + 4/7.11 + 3/11.14 + 1/14.15 + 13/15.28)
B = 7(1/2 - 1/7 + 1/7 - 1/11 +......+ 1/15 - 1/28)
B = 7(1/2 - 1/28)
B = 7 . 13/28
B = 13/4
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nguyễn mai phương đúng rồi đó các bạn
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Xem thêm câu trả lời
10 tháng 11 2023 lúc 21:45
dfrac{-1}{20}+dfrac{-1}{30}+dfrac{-1}{42}+dfrac{-1}{56}+dfrac{-1}{72}+dfrac{-1}{90}
dfrac{5}{2.1}+dfrac{4}{1.11}+dfrac{3}{11.2}+dfrac{1}{2.15}+dfrac{13}{15.4}
cíu mình 2 bài này với mình ko biết làm
Đọc tiếp
\(\dfrac{-1}{20}\)+\(\dfrac{-1}{30}\)+\(\dfrac{-1}{42}\)+\(\dfrac{-1}{56}\)+\(\dfrac{-1}{72}\)+\(\dfrac{-1}{90}\)=
\(\dfrac{5}{2.1}\)+\(\dfrac{4}{1.11}\)+\(\dfrac{3}{11.2}\)+\(\dfrac{1}{2.15}\)+\(\dfrac{13}{15.4}\)=
cíu mình 2 bài này với mình ko biết làm
Không dùng máy tinh bỏ túi.Tính hợp lí:
a,4/2.4+4/4.6+4/6.8+......+4/2012.2014
b,5/2.1+4/1.11+3/11.2+1/2.15+13/15.4
c,(2/3+2/7-1/14):(-1-3/7+3/28)
d,1/10+-1/20+-1/30+-1/42+-1/56+-1/72+-1/90
a,A=4/2.4+4/4.6+4/6.8+......+4/2012.2014
\(\Rightarrow\frac{1}{2}A=\frac{2}{2\cdot4}+\frac{2}{4\cdot6}+...+\frac{2}{2012\cdot2014}\)
\(\Rightarrow\frac{1}{2}A=\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+...+\frac{1}{2012}-\frac{1}{2014}\)
\(\Rightarrow\frac{1}{2}A=\frac{1}{2}-\frac{1}{2014}\)
\(\Rightarrow A=1-\frac{1}{1007}\)
\(\Rightarrow A=\frac{1006}{1007}\)
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không quy đồng hãy tính hợp lí các tổng sau :
a) A = \(\frac{-1}{20}+\frac{-1}{30}+\frac{-1}{42}+\frac{-1}{56}+\frac{-1}{72}+\frac{-1}{90}\)
b) B = \(\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)
\(a,A=\frac{-1}{20}+\frac{-1}{30}+\frac{-1}{42}+\frac{-1}{56}+\frac{-1}{72}+\frac{-1}{90}\)
\(=\frac{-1}{4.5}+\frac{-1}{5.6}+\frac{-1}{6.7}+\frac{-1}{7.8}+\frac{-1}{8.9}+\frac{-1}{9.10}\)
\(=\frac{-1}{4}+\frac{1}{5}-\frac{1}{5}+\frac{1}{6}-...-\frac{1}{9}+\frac{1}{10}\)
\(=-\frac{1}{4}+\frac{1}{10}\)
\(=-\frac{3}{20}\)
\(b,B=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)
\(\frac{B}{7}=\frac{5}{2.7}+\frac{4}{11.7}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.28}\)
\(=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-....-\frac{1}{28}\)
\(=\frac{1}{2}-\frac{1}{28}=\frac{13}{28}\)
a) \(A=\frac{-1}{20}+\frac{-1}{30}+\frac{-1}{42}+\frac{-1}{56}+\frac{-1}{72}+\frac{-1}{90}\)
\(\Rightarrow-1.A=\frac{1}{20}+\frac{1}{30}+........+\frac{1}{90}\)
\(=\frac{1}{4.5}+\frac{1}{5.6}+........+\frac{1}{9.10}\)
\(=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+........+\frac{1}{9}-\frac{1}{10}=\frac{1}{4}-\frac{1}{10}=\frac{3}{20}\)
\(\Rightarrow A=\frac{3}{20}:\left(-1\right)=\frac{-3}{20}\)
b) \(B=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)
\(\Rightarrow\frac{1}{7}B=\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.28}\)
\(=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}\)
\(=\frac{1}{2}-\frac{1}{28}=\frac{13}{28}\)
\(\Rightarrow B=\frac{13}{28}:\frac{1}{7}=\frac{13}{28}.7=\frac{13}{4}\)
Bài giải
a, \(A=\frac{-1}{20}+\frac{-1}{30}+\frac{-1}{42}+\frac{-1}{56}+\frac{-1}{72}+\frac{-1}{90}\)
\(-1A=\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\)
\(-1A=\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+\frac{1}{7\cdot8}+\frac{1}{8\cdot9}+\frac{1}{9\cdot10}\)
\(-1A=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\)
\(-1A=\frac{1}{4}-\frac{1}{10}\)
\(-1A=\frac{3}{20}\)
\(A=\frac{3}{20\text{ }}\text{ : }\left(-1\right)=-\frac{3}{20}\)
b, \(B=\frac{5}{2\cdot1}+\frac{4}{1\cdot11}+\frac{3}{11\cdot2}+\frac{1}{2\cdot15}+\frac{13}{15\cdot4}\)
\(\frac{1}{7}B=\frac{5}{2\cdot7}+\frac{4}{7\cdot11}+\frac{3}{11\cdot14}+\frac{1}{14\cdot15}+\frac{13}{15\cdot28}\)
\(\frac{1}{7}B=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}\)
\(\frac{1}{7}B=\frac{1}{2}-\frac{1}{28}\)
\(\frac{1}{7}B=\frac{13}{28}\)
\(B=\frac{13}{28}\text{ : }\frac{1}{7}=\frac{13}{4}\)
Xem thêm câu trả lời
cho A=102004+1/102005+1 và B=102005+1/102006+1
hãy so sánh A và B
Giải:
A=102004+1/102005+1
10A=102005+10/102005+1
10A=102005+1+9/102005+1
10A=1+9/102005+1
Tương tự:
B=102005+1/102006+1
10B=1+9/102006+1
Vì 9/102005+1>9/102006+1 nên 10A>10B
⇒A>B
Chúc bạn học tốt!
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tinh nhanh
a) A=(-1).(-1)^2.(-1)^3.(-1)^4....(-1)^2010.(-1)^2011
b) B=70.(131313/565656+131313/727272+131313/909090)
d)D= -1/20+ -1/30+ -1/42+ -1/56+ -1/72+ -1/90
e) E= 5/2.1+4/1.11+3/11.2+1/2.15+13/15.4
Cho A = 102004 +1/102005 +1 và B = 102005 + 1/102006 +1
So sánh A và B
\(10A=10.\dfrac{10^{2004}+1}{10^{2005}+1}=\dfrac{10^{2005}+10}{10^{2005}+1}=1+\dfrac{9}{10^{2005}+1}\\ 10B=10.\dfrac{10^{2005}+1}{10^{2006}+1}=\dfrac{10^{2006}+10}{10^{2006}+1}=1+\dfrac{9}{10^{2006}+1}\)
vì \(\dfrac{9}{10^{2005}+1}>\dfrac{9}{10^{2006}+1}\Rightarrow10A>10B\Rightarrow A>B\)
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Không quy đồng hãy tính hợp lý các tổng sau :
a) A=\(\frac{-1}{20}+\frac{-1}{30}+\frac{-1}{42}+\frac{-1}{56}+\frac{-1}{72}+\frac{-1}{90}\)
b) B=\(\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)