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\(A=\frac{1}{30}+\frac{1}{42}+...+\frac{1}{210}\)
\(A=\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{14.15}\)
\(A=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{14}-\frac{1}{15}\)
\(A=\frac{1}{5}-\frac{1}{15}\)
Tự tính nha :)
\(B=\frac{2}{2.3}+\frac{2}{3.4}+...+\frac{2}{99.100}\)
\(B=2\left(\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{99.100}\right)\)
\(B=2\left(\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{99.100}\right)\)
\(B=2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{99}-\frac{1}{100}\right)\)
\(B=2\left(\frac{1}{2}-\frac{1}{100}\right)\)
Tự làm
A=1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7+1/7.8
\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{7}-\frac{1}{8}\)
\(A=1-\frac{1}{8}\)
\(A=\frac{7}{8}\)
B=3/12+3/20+3/30+3/42+3/56+3/72+3/90+3/110+3/132
\(B=\frac{3}{3.4}+\frac{3}{4.5}+....+\frac{3}{11.12}\)
\(B=3\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{11}-\frac{1}{12}\right)\)
\(B=3\left(\frac{1}{3}-\frac{1}{12}\right)\)
\(B=3\times\frac{1}{4}\)
\(B=\frac{3}{4}\)
tự làm tiếp nhé tui ngủ đây
\(A=\frac{1}{6}+\frac{1}{12}+...+\frac{1}{110}=\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{10\cdot11}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{10}-\frac{1}{11}=\left(\frac{1}{2}-\frac{1}{11}\right)+\left(\frac{1}{3}-\frac{1}{3}\right)+...+\left(\frac{1}{10}-\frac{1}{10}\right)\)\(=\left(\frac{1}{2}-\frac{1}{11}\right)+0+...+0=\frac{11}{22}-\frac{2}{22}=\frac{9}{22}\)
\(A=\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}\)
\(=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}+\frac{1}{10.11}\)
\(=\frac{1}{2}-\frac{1}{11}\)
\(=\frac{9}{22}\)
\(A=\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}\)
\(A=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}+\frac{1}{10.11}\)
\(A=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{11}\)
\(A=\left(\frac{1}{2}-\frac{1}{11}\right)+0+...+0\)
\(A=\frac{11}{22}-\frac{2}{22}\)
\(A=\frac{9}{22}\)
\(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{99\cdot100}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{99}-\frac{1}{100}\)
\(=1-\frac{1}{100}\)
\(=\frac{99}{100}\)
1/20 + 1/30 + 1/42 + ... + 1/156
= 1/4.5 + 1/5.6 + 1/6.7 + .... + 1/12.13
= 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + ... + 1/12 - 1/13
= 1/4 - 1/13
= 9/52
\(=\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}+\frac{1}{10.11}+\frac{1}{11.12}+\frac{1}{12.13}\)
\(=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+....+\frac{1}{12}-\frac{1}{13}\)
\(=\frac{1}{4}-\frac{1}{13}=\frac{9}{52}\)
****
Ta viết lại biểu thức A như sau:
\(A=-\left(\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+...+\dfrac{1}{11.12}\right)\)
\(A=-\left(\dfrac{5-4}{4.5}+\dfrac{6-5}{5.6}+\dfrac{7-6}{6.7}+...+\dfrac{12-11}{11.12}\right)\)
\(A=-\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+...+\dfrac{1}{11}-\dfrac{1}{12}\right)\)
\(A=-\left(\dfrac{1}{4}-\dfrac{1}{12}\right)\)
\(A=-\dfrac{1}{6}\)
A= 1/1.2 + 1/2.3 + 1/3.4+...+ 1/99.100
=1-1/2+1/2-1/3+1/3-1/4+...+1/99-1/100
=1-1/100
=99/100
B=1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90 + 1/110
=1/4.5+1/5.6+1/6.7+1/7.8+1/8.9+1/9.10+1/10.11
=1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11
=1/4-1/11
=7/44
L-i-k-e nha bn hiền
A=1/1.2+1/2.3+...+1/99.100
A=1-1/2+1/2-1/3+1/3-...+1/99-1/100
A=1-1/100
A=99/100
Vậy A=99/100
A=1/1.2 + 1/1.3 +...+1/99.100
=(1/1-1/2)+(1/2-1/3)+...+(1/99-1/100)
=1-1/2+1/2-1/3+...+1/99-1/100
=1-1/100
=99/100
B=1/20+1/30+...+1/110
=1/4.5+1/5.6+...+1/10.11
=(1/4-1/5)+(1/5-1/6)+...+(1/10-1/11)
=1/4-1/5+1/5-1/6+...+1/10-1/11
=1/4-1/11
=7/44
=33.100.101 đó, cho mình nha!!!
A=1/1.2+1/2.3+1/3.4+...+1/99.100
A=1-1/2+1/2-1/3+1/3-1/4+...=1/99-1/100
A=1-1/100
A=99/100
A=1/1-1/2+1/3-1/4+...+1/99-1/100
=1-1/100
=100/100-1/100
=99/100
B=1/20+1/30+1/42+1/56+1/72+1/90+1/110
=1/4.5+1/5.6+1/6.7+1/7.8+1/8.9+1/9.10+1/10.11
=1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11
=1/4-1/11
=11/44-4/44
=7/44
A= 1/1.2+1/2.3+1/3.4+... + 1/99.100
A= 1-1/2+1/2-1/3+1/3-1/4+... + 1/99-1/100
A=1-1/100
A=99/100
B=1/20+1/30+1/42+1/56+1/72+1/90+1/110
B=1/4.5+1/5.6+1/6.7+1/7.8+1/8.9+1/9.10+1/10.11
B=1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11
B=1/4-1/11
B=7/44
Vậy các cậu Ơi cho mình hỏi:1+1=mấy
tính tổng 2/2.3+2/3.4+...+2/98.99
nhanh dùm với
óc chó
=1-1/2+1/2-1/3+1/3-1/4+......+1/99-1/100
=1-1/100
=99/100
7/44 ha
Có làm thì mới có ăn. Những cái loại không làm mà đòi có ăn, là ăn đầu b** với ăn cứt nhá...Đấy nói vậy đi cho dễ hiểu.
\(\sqrt[]{\frac{ }{ }\hept{\begin{cases}\\\\\end{cases}}\orbr{\begin{cases}\\\end{cases}}^2_{ }\sinh\cos\sin\leftarrow\approx}\)
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