Tính nhanh ( hợp lí )
\(\frac{7}{3.4}-\frac{9}{4.5}+\frac{11}{5.6}-\frac{13}{6.7}+\frac{15}{7.8}-\frac{17}{8.9}-\frac{19}{9.10}+\frac{21}{10.11}\)
Tính :
A=\(\frac{7}{3.4}\)-\(\frac{9}{4.5}\)+\(\frac{11}{5.6}-\frac{13}{6.7}+\frac{15}{7.8}-\frac{17}{8.9}+\frac{19}{9.10}\)
bạn tìm 1 số để nhân cả tử cả mẫu ra để tử ra 1 so chung nha rồi tách thôi
Tính:
A = \(\frac{7}{3.4}\) - \(\frac{9}{4.5}\) + \(\frac{11}{5.6}\) - \(\frac{13}{6.7}\) + \(\frac{15}{7.8}\) - \(\frac{17}{8.9}\) + \(\frac{19}{9.10}\)
A=7/3.4 - 9/4.5 + 11/5.6 - 13/6.7 + 15/7.8 -17/8.9+19/9.10
=(1/3+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)+(1/7+1/8)
-(1/8+1/9)+(1/9+1/10)
=1/3-1/5+1/5-1/7+1/7-1/9+1/9+1/10
=1/3+1/10
=13/30
Vậy A = 13/30
\(A=\frac{7}{3.4}-\frac{9}{4.5}+\frac{11}{5.6}-\frac{13}{6.7}+\frac{15}{7.8}-\frac{17}{8.9}+\frac{19}{9.10}\)
\(=\frac{1}{3}+\frac{1}{4}-\frac{1}{4}-\frac{1}{5}+\frac{1}{5}+\frac{1}{6}-\frac{1}{6}-\frac{1}{7}+\frac{1}{7}+\frac{1}{8}-\frac{1}{8}-\frac{1}{9}+\frac{1}{9}+\frac{1}{10}\)=\(\frac{1}{3}+\frac{1}{10}=\frac{13}{30}\)
Tính nhanh
\(B=\frac{1}{3.4}-\frac{1}{4.5}-\frac{1}{5.6}-\frac{1}{6.7}-\frac{1}{7.8}-\frac{1}{8.9}-\frac{1}{9.10}\)
\(B=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+....+\frac{1}{9}-\frac{1}{10}\)
\(B=\frac{1}{3}-\frac{1}{10}\)
\(B=\frac{7}{30}\)
Tính nhanh:
C=\(\frac{7}{3.4}\)-\(\frac{9}{4.5}\)+\(\frac{11}{5.6}\)-\(\frac{13}{6.7}\)+\(\frac{15}{7.8}\)-\(\frac{17}{8.9}\)+\(\frac{19}{9.10}\)
C=\(\frac{7}{3.4}\)-\(\frac{9}{4.5}\)+\(\frac{11}{5.6}\)+\(\frac{13}{6.7}\)+\(\frac{15}{7.8}\)-\(\frac{17}{8.9}\)+\(\frac{19}{9.10}\)
=\(\frac{1}{3}\)+\(\frac{1}{4}\)-\(\frac{1}{4}\)-\(\frac{1}{5}\)+\(\frac{1}{5}\)+\(\frac{1}{6}\)-\(\frac{1}{6}\)-\(\frac{1}{7}\)+\(\frac{1}{7}\)+\(\frac{1}{8}\)-\(\frac{1}{8}\)-\(\frac{1}{9}\)+\(\frac{1}{9}\)+\(\frac{1}{10}\)
=\(\frac{1}{3}\)+\(\frac{1}{10}\)=\(\frac{13}{30}\)
fddddddddddddddddddddddddddddddddddddddddđ
Cho A = \(\frac{7}{3.4}\) - \(\frac{9}{4.5}\) + \(\frac{11}{5.6}\) - \(\frac{13}{6.7}\) + \(\frac{15}{7.8}\) - \(\frac{17}{8.9}\) + \(\frac{19}{9.10}\)
Hãy tính A.
Các bạn giúp mình với, nhanh nhé, mình đang cần gấp !
Bài này mình mới nghĩ ra được đến đây thôi à, các bạn xem rồi giúp mình giải phần tiếp theo nhé !
A = \(\frac{7}{3.4}\) - \(\frac{9}{4.5}\) + \(\frac{11}{5.6}\) - \(\frac{13}{6.7}\) + \(\frac{15}{7.8}\) - \(\frac{17}{8.9}\) + \(\frac{19}{9.10}\)
A = \(\frac{6+1}{3.4}\) - \(\frac{10-1}{4.5}\) + \(\frac{10+1}{5.6}\) - \(\frac{14-1}{6.7}\) + \(\frac{14+1}{7.8}\) - \(\frac{18-1}{8.9}\) + \(\frac{18+1}{9.10}\)
A = \(\frac{6}{3.4}\) + \(\frac{1}{3.4}\) - \(\frac{10}{4.5}\) - \(\frac{1}{4.5}\) + \(\frac{10}{5.6}\) + \(\frac{1}{5.6}\) - \(\frac{14}{6.7}\) - \(\frac{1}{6.7}\) + \(\frac{14}{7.8}\) + \(\frac{1}{7.8}\) - \(\frac{18}{8.9}\) - \(\frac{1}{8.9}\) + \(\frac{18}{9.10}\) + \(\frac{1}{9.10}\)
Mình làm được đến đây thôi, các bạn giúp mình nhé ! Thanks !
Đường cùng rồi làm đại thôi, từ đề suy ra nha
=> 7.9.11.13.15.17.19.(\(\frac{1}{3.4}-\frac{1}{4.5}+\frac{1}{5.6}-\frac{1}{6.7}+\frac{1}{7.8}-\frac{1}{8.9}+\frac{1}{9.10}\) )
chịu thua
Cái này họ cho trên violympic, mình không bít làm, bấm máy tính ra \(\frac{13}{30}\) đó!!!
Tính theo cách hợp lí:
M = \(\frac{1}{9.10}-\frac{1}{8.9}-\frac{1}{7.8}-\frac{1}{6.7}-\frac{1}{5.6}-\frac{1}{4.5}-\frac{1}{3.4}-\frac{1}{2.3}-\frac{1}{1.2}\)
\(M=\frac{1}{9.10}-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{8.9}\right)=\frac{1}{90}-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{8}-\frac{1}{9}\right)=\frac{1}{90}-\left(1-\frac{1}{9}\right)=\frac{1}{90}-\frac{8}{9}=-\frac{79}{90}\)
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Cho A = \(\frac{7}{3.4}\) - \(\frac{9}{4.5}\) + \(\frac{11}{5.6}\) - \(\frac{13}{6.7}\) + \(\frac{15}{7.8}\) - \(\frac{17}{8.9}\) + \(\frac{19}{9.10}\)
Hãy tính A.
Các bạn giúp mình với nhé ! Thanks !
tính
\(B=\frac{1}{3.4}-\frac{1}{4.5}-\frac{1}{5.6}-\frac{1}{6.7}-\frac{1}{7.8}-\frac{1}{8.9}-\frac{1}{9.10}\)
ai nhanh tik luôn
\(B=\frac{1}{3.4}-\frac{1}{4.5}-\frac{1}{5.6}-\frac{1}{6.7}-\frac{1}{7.8}-\frac{1}{8.9}-\frac{1}{9.10}\)
\(\Rightarrow B=\frac{1}{3.4}-\left(\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\right)\)
\(\Rightarrow B=\frac{1}{12}-\left(\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\right)\)
\(\Rightarrow B=\frac{1}{3}-\frac{1}{4}-\left(\frac{1}{4}-\frac{1}{10}\right)\)
\(\Rightarrow B=\frac{1}{12}-\frac{6}{40}\)
\(\Rightarrow B=\frac{-1}{15}\)