Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
Bạn tự ghi lại đề nha !
A = \(\frac{1}{3}\)+ \(\left(\frac{1}{42}+\frac{1}{56}+...+\frac{1}{600}\right)\)
A = \(\frac{1}{3}\)+ \(\left(\frac{1}{6.7}+\frac{1}{7.8}+...+\frac{1}{24.25}\right)\)
A = \(\frac{1}{3}\)+ \(\left(\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{24}-\frac{1}{25}\right)\)
A = \(\frac{1}{3}\)+ \(\left(\frac{1}{6}-\frac{1}{25}\right)\)
A = \(\frac{1}{3}\)+ \(\frac{19}{150}\)
A = \(\frac{23}{50}\).
Em xem lại đề bài nhé! có thể tham khảo bài dưới đây:
\(A=\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+...+\frac{1}{600}\)
\(=\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+...+\frac{1}{24.25}\)
\(=\frac{6-5}{5.6}+\frac{7-6}{6.7}+\frac{8-7}{7.8}+...+\frac{25-24}{25.24}\)
\(=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{24}-\frac{1}{25}\)
\(=\frac{1}{5}-\frac{1}{25}=\frac{4}{25}\)
Nếu đề bài không bị sai
\(A=\frac{1}{3}+\left(\frac{1}{42}+...+\frac{1}{600}\right)\)
\(=\frac{1}{3}+\left(\frac{1}{6.7}+\frac{1}{7.8}+...+\frac{1}{24.25}\right)\)
\(=\frac{1}{3}+\left(\frac{1}{6}-\frac{1}{25}\right)\)
Tự làm nốt nhé!
\(\frac{27}{20}-\frac{33}{30}+\frac{39}{42}-\frac{45}{56}\)
\(=(\frac{27}{20}-\frac{11}{10})+(\frac{13}{14}-\frac{45}{56})\)
\(=\frac{1}{4}+\frac{1}{8}\)
\(=\frac{3}{8}\)
\(\frac{27}{20}\)-\(\frac{33}{30}\)+\(\frac{39}{42}\)-\(\frac{45}{56}\)
=\(\frac{1}{4}+\frac{1}{8}\)
=\(\frac{3}{8}\)
a) 4 x 8 x ( 56 + 44) - 3200
= 32 x 100 - 3200
= 0
b) \(\frac{3+2}{60}\)+ \(\frac{4+3}{168}\)
= \(\frac{5}{60}\)+ \(\frac{7}{168}\)
= \(\frac{1}{8}\)
A=1/2x3 + 1/3x4 + 1/4x5 + ... + 1/9x10
A=1/2 - 1/3 + 1/3 - 1/4+ 1/4 - 1/5+...+ 1/9 - 1/10
A= 1/2 - 1/10
Vậy A=2/5
Chúc bạn học tốt~~
\(\frac16+\frac{1}{12}+\frac{1}{20}+\cdots+\frac{1}{72}+\frac{1}{90}\)
\(=\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+\ldots+\frac{1}{8\times9}+\frac{1}{9\times10}\)
\(=\frac12-\frac13+\frac13-\frac14+\cdots+\frac18-\frac19+\frac19-\frac{1}{10}\)
\(=\frac12-\frac{1}{10}=\frac{4}{10}=\frac25\)
\(A=-\frac{1}{20}+-\frac{1}{30}+-\frac{1}{42}+-\frac{1}{56}+-\frac{1}{72}+-\frac{1}{90}\)
\(\Rightarrow A=-1\left(\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{9.10}\right)\)
\(A=-1\left(\frac{1}{4}-\frac{1}{10}\right)\)
\(\Rightarrow A=-\frac{3}{20}\)
\(A=\frac{-1}{20}-\frac{-1}{30}+\frac{-1}{42}+\frac{-1}{56}+\frac{-1}{72}+\frac{-1}{90}\)
\(A=-\left(\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\right)\)
\(A=-\left(\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{9}-\frac{1}{10}\right)\)
\(A=-\left(\frac{1}{4}-\frac{1}{10}\right)\)
\(A=\frac{-3}{20}\)
#
56 × 42 : 100
Đáp án A