Tính bằng phương pháp hợp lí
a> C = \(\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+\frac{3}{10\cdot13}+...+\frac{3}{73\cdot76}\) b> D = \(\frac{5}{10\cdot11}+\frac{5}{11\cdot12}+\frac{5}{12\cdot13}+...+\frac{5}{99\cdot100}\)
NHANH LÊN MÌNH CẦN GẤP
Những câu hỏi liên quan
\(A=\frac{7}{10\cdot11}+\frac{7}{11\cdot12}+\frac{7}{12\cdot13}+...+\frac{7}{69\cdot70}\)
\(B=\frac{1}{25\cdot27}+\frac{1}{27\cdot29}+\frac{1}{29\cdot30}+...+\frac{1}{73\cdot75}\)
\(C=\frac{4}{2\cdot4}+\frac{4}{4\cdot6}+\frac{4}{6\cdot8}+...3+\frac{4}{2008\cdot2010}\)
\(A=\frac{7}{10.11}+\frac{7}{11.12}+\frac{7}{12.13}+...+\frac{7}{69.70}\)
\(=7.\frac{1}{10.11}+7.\frac{1}{11.12}+7.\frac{1}{12.13}+...+7.\frac{1}{69.70}\)
\(=7.\left(\frac{1}{10.11}+\frac{1}{11.12}+\frac{1}{12.13}+...+\frac{1}{69.70}\right)\)
\(=7.\left(\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}+\frac{1}{12}-\frac{1}{13}+...+\frac{1}{69}-\frac{1}{70}\right)\)
\(=7.\left(\frac{1}{10}-\frac{1}{70}\right)=7.\frac{3}{35}=\frac{3}{5}\)
Đúng 0
Bình luận (0)
\(A=7.\left(\frac{1}{10}-\frac{1}{70}\right)\)
\(=\frac{6}{70}\)
\(=\frac{3}{35}\)
Đúng 0
Bình luận (0)
\(B=\frac{1}{2}.\left(\frac{2}{25.27}+\frac{2}{27.29}+...+\frac{2}{73.75}\right)\)
\(=\frac{1}{2}.\left(\frac{1}{25}-\frac{1}{75}\right)\)
\(=\frac{1}{2}.\frac{2}{75}\)
\(=\frac{1}{75}\)
=
Đúng 0
Bình luận (0)
Xem thêm câu trả lời
\(\frac{ }{\frac{4}{3\cdot7}+\frac{5}{7\cdot12}+\frac{1}{12\cdot13}+\frac{7}{13\cdot20}+\frac{3}{20\cdot23}}\)
làm cách thủ công đi
\(=\frac{20}{69}\)
Đúng 0
Bình luận (0)
Xem thêm câu trả lời
\(\frac{4}{3\cdot7}+\frac{5}{7\cdot12}+\frac{1}{12\cdot13}+\frac{7}{13\cdot20}+\frac{3}{20\cdot23}\)
\(\frac{4}{3.7}+\frac{5}{7.12}+\frac{1}{12.13}+\frac{7}{13.20}+\frac{3}{20.23}=\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{12}+...+\frac{1}{20}-\frac{1}{23}=\frac{1}{3}-\frac{1}{23}=\frac{20}{69}\)
Đúng 0
Bình luận (0)
\(\frac{4}{3\cdot7}+\frac{5}{7\cdot12}+\frac{1}{12\cdot13}+\frac{7}{13\cdot20}+\frac{8}{20\cdot28}\)
\(\frac{4}{3\cdot7}+\frac{5}{7.12}+..+\frac{8}{20\cdot28}\)
\(=\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{12}+...+\frac{1}{20}-\frac{1}{28}\)
\(=\frac{1}{3}-\frac{1}{28}+0+...+0\)
\(=\frac{25}{84}\)
Đúng 0
Bình luận (0)
\(=\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{12}+...+\frac{1}{20}-\frac{1}{28}\)
\(=\frac{1}{3}-\frac{1}{28}\)
\(=\frac{25}{84}\)
Đúng 0
Bình luận (0)
giải phương trìnha,(frac{1}{1cdot2}+frac{1}{2cdot3}+frac{1}{3cdot4}+frac{1}{9cdot10})(x-1)+frac{1}{10}xx-frac{9}{10}b,frac{x+1}{1}+frac{2x+3}{3}+frac{3x+5}{5}+frac{20x+39}{39}22+frac{4}{3}+frac{6}{5}+frac{40}{39}c,(x-10)+(x-19)+(x-18)+...+100+101101d,(frac{1}{1cdot51}+frac{1}{2cdot52}+frac{1}{3cdot53}+...+frac{1}{10cdot60})xfrac{1}{1cdot11}+frac{1}{1cdot12}+frac{1}{1cdot13}
Đọc tiếp
giải phương trình
a,(\(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{9\cdot10}\))(x-1)+\(\frac{1}{10}x\)=\(x-\frac{9}{10}\)
b,\(\frac{x+1}{1}+\frac{2x+3}{3}+\frac{3x+5}{5}+\frac{20x+39}{39}=22+\frac{4}{3}+\frac{6}{5}+\frac{40}{39}\)
c,(x-10)+(x-19)+(x-18)+...+100+101=101
d,(\(\frac{1}{1\cdot51}+\frac{1}{2\cdot52}+\frac{1}{3\cdot53}+...+\frac{1}{10\cdot60}\))x=\(\frac{1}{1\cdot11}+\frac{1}{1\cdot12}+\frac{1}{1\cdot13}\)
\(\frac{4}{1\cdot3\cdot5}+\frac{4}{3\cdot5\cdot7}+\frac{4}{5\cdot7\cdot9}+\frac{4}{7\cdot9\cdot11}+\frac{4}{9\cdot11\cdot13}\)
giúp mk nha các bn
\(\frac{4}{1\cdot3\cdot5}+\frac{4}{3\cdot5\cdot7}+\frac{4}{5\cdot7\cdot9}+\frac{4}{7\cdot9\cdot11}+\frac{4}{9\cdot11\cdot13}\)
\(=\frac{1}{1.3}-\frac{1}{3.5}+\frac{1}{3.5}-\frac{1}{5.7}+...+\frac{1}{9.11}-\frac{1}{11.13}\)
\(=\frac{1}{1.3}-\frac{1}{11.13}\)
\(=\frac{1}{3}-\frac{1}{143}\)
\(=\frac{140}{429}\)
Đúng 0
Bình luận (0)
\(\frac{3}{1\cdot4}+\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+\frac{3}{10\cdot13}+\frac{3}{13\cdot16}\)
\(\frac{15}{16}\)nha bạn
úm ba la xin tích
Đúng 0
Bình luận (0)
\(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+\frac{3}{13.16}\)
\(=1\left(\frac{1}{1}-\frac{1}{16}\right)\)
\(=1.\frac{15}{16}=\frac{15}{16}\)
Đúng 0
Bình luận (0)
3/1.4+3/4.7+3/7.10+3/10.13+3/13.16=1/1-1/4+1/4-1/7+1/7-1/10+1/10-1/13+1/13-1/16=1-1/16=15/15
Đúng 0
Bình luận (0)
Tìm a biết :
A=\(\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+\frac{3}{10\cdot13}+..........+\frac{3}{94\cdot97}+\frac{3}{97\cdot100}\)=??????????????????
A = \(\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{94.97}+\frac{3}{97.100}\)
\(\Rightarrow A=\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{94}-\frac{1}{97}+\frac{1}{97}-\frac{1}{100}\)
\(\Rightarrow A=\frac{1}{4}-\frac{1}{100}\)
\(\Rightarrow A=\frac{24}{100}=\frac{6}{25}\)
Đúng 0
Bình luận (0)
A=3/4-3/7+3/7-3/10+3/10-3/13+.........+3/94-3/97+3/97-3/100
Bây giờ loại các phân số giống nhau
A=3/4-3/100
A=18/25
Đúng 0
Bình luận (0)
left(3cdot x-0,8right):x+14,5151,2cdot(frac{2,4cdot x-0,23}{x}-0,051,44frac{1}{1cdot4}+frac{1}{4cdot7}+frac{1}{7cdot10}+...+frac{1}{97cdot100}frac{0,33cdot x}{2009}x-frac{20}{11cdot13}-frac{20}{13cdot15}-...-frac{20}{53cdot55}frac{3}{11}left(frac{10}{56}+frac{10}{140}+frac{10}{260}+...+frac{10}{1400}right)cdot xfrac{5}{14}Các bạn ơi trả lời giùm mình với nhé, cần gấp.
Đọc tiếp
\(\left(3\cdot x-0,8\right):x+14,5=15\)
1,2\(\cdot\)(\(\frac{2,4\cdot x-0,23}{x}\)\(-0,05=1,44\)
\(\frac{1}{1\cdot4}+\frac{1}{4\cdot7}+\frac{1}{7\cdot10}+...+\frac{1}{97\cdot100}=\frac{0,33\cdot x}{2009}\)
\(x\)-\(\frac{20}{11\cdot13}-\frac{20}{13\cdot15}-...-\frac{20}{53\cdot55}=\frac{3}{11}\)
\(\left(\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+...+\frac{10}{1400}\right)\)\(\cdot x=\frac{5}{14}\)
Các bạn ơi trả lời giùm mình với nhé, cần gấp.
\(\frac{1}{1.4}+\frac{1}{4.7}+\frac{1}{7.10}+....+\frac{1}{97.100}=\frac{0,33.x}{2009}\)
\(\Leftrightarrow\frac{1}{3}\cdot\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+....+\frac{1}{97}-\frac{1}{100}\right)=\frac{0,33.x}{2009}\)
\(\Leftrightarrow\frac{1}{3}\cdot\left(1-\frac{1}{100}\right)=\frac{0,33.x}{2009}\)
\(\Leftrightarrow\frac{1}{3}\cdot\frac{99}{100}=\frac{0,33.x}{2009}\)
\(\Leftrightarrow\frac{33}{100}=\frac{0,33.x}{2009}\)
\(\Leftrightarrow x=\frac{0,33\times100}{0,33}=100\)
Đúng 0
Bình luận (0)