Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
\(\frac{-1}{20}+\frac{-1}{30}+\frac{-1}{42}+\frac{-1}{56}+\frac{-1}{72}+\frac{-1}{90} \)\(\frac{-1}{90}\)
\(=\frac{-1}{4.5}+\frac{-1}{5.6}+\frac{-1}{6.7}+\frac{-1}{7.8}+\frac{-1}{8.9}+\frac{-1}{9.10}\)
\(=\frac{-1}{4}-\frac{-1}{5}+\frac{-1}{5}-\frac{-1}{6}+\frac{-1}{6}-\frac{-1}{7}+\frac{-1}{7}-\frac{-1}{8}+\frac{-1}{8}-\frac{-1}{9}+\frac{-1}{9}-\frac{-1}{10}\)
\(=\frac{-1}{4}-\frac{-1}{10} \)\(=\frac{-3}{20}\)
\(\frac{-1}{20}+\frac{-1}{30}+\frac{-1}{42}+\frac{-1}{56}+\frac{-1}{72}+\frac{-1}{90}\)
= \(\frac{-1}{4}-\frac{-1}{10}\)
=\(\frac{-3}{20}\)
\(A=-\frac{1}{20}+-\frac{1}{30}+-\frac{1}{42}+-\frac{1}{56}+-\frac{1}{72}+-\frac{1}{90}\)
\(\Rightarrow A=-1\left(\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{9.10}\right)\)
\(A=-1\left(\frac{1}{4}-\frac{1}{10}\right)\)
\(\Rightarrow A=-\frac{3}{20}\)
\(A=\frac{-1}{20}-\frac{-1}{30}+\frac{-1}{42}+\frac{-1}{56}+\frac{-1}{72}+\frac{-1}{90}\)
\(A=-\left(\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\right)\)
\(A=-\left(\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{9}-\frac{1}{10}\right)\)
\(A=-\left(\frac{1}{4}-\frac{1}{10}\right)\)
\(A=\frac{-3}{20}\)
#
A= \(\frac{-1}{4\cdot5}+\frac{-1}{5\cdot6}+\frac{-1}{6\cdot7}+\frac{-1}{7\cdot8}+\frac{-1}{8\cdot9}+\frac{-1}{9\cdot10}\)
=\(-1\left(\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+\frac{1}{7\cdot8}+\frac{1}{8\cdot9}+\frac{1}{9\cdot10}\right)\)
=\(-1\left(\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{9}-\frac{1}{10}\right)\)
=\(-1\left(\frac{1}{4}-\frac{1}{10}\right)\)
=\(-1\cdot\frac{3}{20}\)
=\(\frac{-3}{20}\)
=\(\frac{-1}{20}\)
a) A = \(\frac{1}{5}\) - \(\frac{1}{4}\)+ \(\frac{1}{6}\)- \(\frac{1}{5}\)+ \(\frac{1}{7}\)-\(\frac{1}{6}\)+\(\frac{1}{8}\)-\(\frac{1}{7}\)+\(\frac{1}{9}\)- \(\frac{1}{8}\)+ \(\frac{1}{10}\)- \(\frac{1}{9}\)
= \(\frac{-1}{4}\)+\(\frac{1}{10}\)= \(\frac{-6}{40}\)= \(\frac{-3}{20}\)
b) B = \(\frac{5}{2.1}\)+ \(\frac{1}{11}\)(4 + \(\frac{3}{2}\)) + \(\frac{1}{2.15}\)(1 + \(\frac{13}{2}\))
= \(\frac{5}{2.1}\)+ \(\frac{1}{11}\).\(\frac{11}{2}\)+ \(\frac{1}{2.15}\).\(\frac{15}{2}\)
= \(\frac{5}{2}\)+ \(\frac{1}{2}\)+ \(\frac{1}{4}\)= 3 + \(\frac{1}{4}\)= \(\frac{13}{4}\)
\(=\frac{1}{2.3}+\frac{1}{3.4}+....+\frac{1}{11.12}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{11}-\frac{1}{12}\)
\(=\frac{1}{2}-\frac{1}{12}\)
\(=\frac{5}{12}\)
bn sẽ tinh theo kieeuranhaan 2 nha xin lỗi mik làm bi này rùi nhưng mik quên mik có sacks xem lại
29 . ( 85 -47) + 85. ( 47-29 )
=29.38+85.18
=1102+1530
=1632
2,7 . 10,5 - 7,3 . 10,5 - 7,3 . 15 + 2,7 . 15
=(2,7+7,3).10,5-(2,7+7,3).15
=10.10,5-10.15
=105-150
=-45
-1/4.5 - 1/5.6 - 1/6.7 - 1/7.8 - 1/8.9 - 1/9/10
= -1/4 - (-1/5)+......+(-1/9)-(-1/10)
= -1/4 - (-1/10)
= -1/4 + 1/10
= -3/20
hoang tu bd sai rui phai dat dau am ra ngoai rui ms tinh