Ta có :
\(A=2.\left(\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}+............+\frac{2}{53.55}\right)\)
\(\Rightarrow A=2.\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+..............+\frac{1}{53}-\frac{1}{55}\right)\)
\(\Rightarrow A=2.\left(\frac{1}{5}-\frac{1}{55}\right)=2.\frac{2}{11}=\frac{4}{11}\)
k nha bạn !!!
4/5.7+4/7.9+4/9.11+...+4/53.55 = ?
Tính Nhanh
\(2\frac{3}{13}\)\(-\frac{5}{9}\)\(-\left(\frac{3}{13}+\frac{4}{9}\right)\frac{ }{ }\)
\(17\frac{4}{16}+\frac{3}{4}-\left(2\frac{3}{12}+75\%\right)\)
\(\frac{6}{5.7}+\frac{6}{7.9}+\frac{6}{9.11}+...+\frac{6}{101.103}+\frac{6}{103.106}\)
\(\frac{2}{4.7}+\frac{2}{7.10}+\frac{2}{10.13}+...+\frac{2}{25.28}\)
bài 1 tính
A = \(\frac{2}{3.5}+\frac{2}{5.7}+..............+\frac{2}{37.39}\); B = \(\frac{4}{5.7}+\frac{4}{7.9}+..........+\frac{4}{59.61}\) ; C = \(\frac{4}{5.9}+\frac{4}{9.13}+.................+\frac{4}{41.45}\) Bài 2 chứng minh : \(\frac{m}{b.\left(b+m\right)}=\frac{1}{b}-\frac{1}{b+m}\)
1) Thực hiện phép tính:
a/ \(\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}+....+\frac{1}{97.99}\)
b/ (\(\frac{201}{202}-\frac{206}{207}+\frac{21}{199}\)) . (\(\frac{1}{3}-\frac{1}{4}-\frac{1}{12}\))
Tìm x:
a) \(\frac{6}{5.7}+\frac{6}{7.9}+\frac{6}{9.11}+...+x=\frac{115}{555}\)
b)\(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{x\left(x+1\right)}=\frac{2015}{2016}\)
Bài 1:Tính bằng cách hợp lý:
a)\(\frac{8.4.125.25+96524+3476}{1+5+9+...+61+62,5-26}\)
b)\(\frac{5+55+555+5555}{9+99+999+9999}\)
c)39,2.27+39,2.43+78,4.15
d)\(\frac{4}{17}.\frac{3}{11}+\frac{8}{11}.\frac{4}{17}-\frac{4}{17}\)
e)(812,1.10,5-91.10,5).(41.11-4100.0,1-41)
Bài 2:Tính nhanh các tổng sau:
a)\(\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}+...+\frac{1}{57.59}\)
b)\(\left(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+\frac{1}{5}+\frac{1}{6}+\frac{1}{7}\right)-\left(\frac{1}{3}+\frac{1}{4}+\frac{1}{5}+\frac{1}{6}+\frac{1}{7}+\frac{1}{8}\right)\)
c)\(\left(1-\frac{1}{2}\right).\left(1-\frac{1}{3}\right).\left(1-\frac{1}{4}\right).\left(1-\frac{1}{5}\right)\cdot...\cdot\left(1-\frac{1}{2012}\right)\)
GẤP!GẤP!GẤP!MAI MIK NỘP RỒI!BẠN NÀO ĐẦU TIÊN MIK TIK CHO NHA!
*Lưu ý:Dấu chấm là dấu nhân đó
Tính giá trị của biểu thức
A =\(\left(\frac{1}{2}+1\right)\times\left(\frac{1}{3}+1\right)\times\left(\frac{1}{4}+1\right)\times....\times\left(\frac{1}{99}+1\right)\)
Chứng tỏ
\(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+....+\frac{2}{97.99}>32\%\)
M = \(\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}+\frac{1}{11.13}\)
TÍNH
Q = \(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}\)
