Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
A=1/7 +1/91 +1/247 + 1/475 + 1/775 + 1/1147
A=1/(1.7)+1/(7.13)+1/(13.19)+...+1/(31...
A=(1/6)*( 1 - 1/7 + 1/7 - 1/13 +... +1/31-1/37)
A=(1/6)*(1-1/37)
A=(1/6)*(36/37)
A=6/37
\(\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+\frac{1}{475}+\frac{1}{755}+\frac{1}{1147}\)
\(=\frac{1}{7}+\frac{1}{7.13}+\frac{1}{13.19}+\frac{1}{19.25}+\frac{1}{25.31}+\frac{1}{31.37}\)
\(=\frac{1}{6}\left(1-\frac{1}{37}\right)\)
\(=\frac{1}{6}.\frac{36}{37}\)
\(=\frac{6}{37}\)
\(\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+\frac{1}{475}+\frac{1}{755}+\frac{1}{1147}\)
\(=\frac{1}{1.7}+\frac{1}{7.13}+\frac{1}{13.19}+\frac{1}{19.25}+\frac{1}{25.31}+\frac{1}{31.37}\)
\(=\frac{1}{6}.\left(\frac{6}{1.7}+\frac{6}{7.13}+\frac{6}{13.19}+\frac{6}{19.25}+\frac{6}{25.31}+\frac{6}{35.37}\right)\)
\(=\frac{1}{6}.\left(1-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+\frac{1}{13}-\frac{1}{19}+\frac{1}{19}-\frac{1}{25}+\frac{1}{25}-\frac{1}{31}+\frac{1}{31}-\frac{1}{37}\right)\)
\(=\frac{1}{6}.\left(1-\frac{1}{37}\right)\)
\(=\frac{1}{6}.\frac{36}{37}=\frac{6}{37}\)
~ Hok tốt ~
C=\(\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+\frac{1}{475}+\frac{1}{775}+\frac{1}{1147}\)
C=\(\frac{1}{6}\left\{\frac{6}{1.7}+\frac{6}{7.13}+\frac{6}{13.19}+...+\frac{6}{31.37}\right\}\)=\(\frac{1}{6}\left(1-\frac{1}{7}+\frac{1}{7}+....+\frac{1}{31}-\frac{1}{37}\right)\)
C=\(\frac{1}{6}\left(1-\frac{1}{37}\right)=\frac{1}{6}.\frac{36}{37}=\frac{36}{222}=\frac{6}{37}\)
D=\(\frac{3}{1.3}+\frac{3}{3.5}+\frac{3}{5.7}+......+\frac{3}{49.51}\)
D=\(\frac{3}{2}\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+.....+\frac{2}{49.51}\right)\)
D=\(\frac{3}{2}\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{49}-\frac{1}{51}\right)\)
D=\(\frac{3}{2}\left(1-\frac{1}{51}\right)=\frac{3}{2}.\frac{50}{51}\)
D=\(\frac{150}{102}\)=\(\frac{25}{17}\)
\(=\frac{1}{1.7}+\frac{1}{7.13}+\frac{1}{13.19}+\frac{1}{19.25}+\frac{1}{25.31}+\frac{1}{31.37}\)
\(=\frac{1}{6}\left(\frac{6}{1.7}+\frac{6}{7.13}+\frac{6}{13.19}+\frac{6}{19.25}+\frac{6}{25.31}+\frac{6}{31.37}\right)\)
\(=\frac{1}{6}\left(1-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+...+\frac{1}{31}-\frac{1}{37}\right)\)
\(=\frac{1}{6}\left(1-\frac{1}{37}\right)=\frac{6}{37}\)
Đặt \(A=\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+\frac{1}{475}+\frac{1}{775}+\frac{1}{1147}\)
\(A=\frac{1}{1\cdot7}+\frac{1}{7\cdot13}+\frac{1}{13.19}+\frac{1}{19.25}+\frac{1}{25.31}+\frac{1}{31.37}\)
\(6A=6\left(\frac{1}{1\cdot7}+\frac{1}{7\cdot13}+\frac{1}{13\cdot19}+\frac{1}{19\cdot25}+\frac{1}{25\cdot31}+\frac{1}{31\cdot37}\right)\)
\(6A=\frac{6}{1.7}+\frac{6}{7.13}+\frac{1}{13.19}+\frac{1}{19.25}+\frac{1}{25.31}+\frac{1}{31.37}\)
\(6A=1-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+\frac{1}{13}-\frac{1}{19}+\frac{1}{19}-\frac{1}{25}+\frac{1}{25}-\frac{1}{31}+\frac{1}{31}-\frac{1}{37}\)
\(6A=1-\frac{1}{37}\)
\(6A=\frac{36}{37}\)
\(A=\frac{36}{37}:6\)
\(A=\frac{6}{37}\)
\(S=\frac{5^2}{1.6}+\frac{5^2}{6.11}+...+\frac{5^2}{26.31}\)
\(S=5.\left(\frac{5}{1.6}+\frac{5}{6.11}+...+\frac{5}{26.31}\right)\)
\(S=5.\left(1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+...+\frac{1}{26}-\frac{1}{31}\right)\)
\(S=5.\left(1-\frac{1}{31}\right)\)
\(S=5.\frac{30}{31}\)
\(S=\frac{150}{31}\)
Câu L bạn thiếu số\(\frac{1}{475}\)
\(L=\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+\frac{1}{475}+\frac{1}{775}+\frac{1}{1147}\)
\(L=\frac{1}{1.7}+\frac{1}{7.13}+\frac{1}{13.19}+\frac{1}{19.25}+\frac{1}{25.31}+\frac{1}{31.37}\)
\(L=\frac{1}{6}.\left(\frac{6}{1.7}+\frac{6}{7.13}+\frac{6}{13.19}+\frac{6}{19.25}+\frac{6}{25.31}+\frac{6}{31.37}\right)\)
\(L=\frac{1}{6}.\left(1-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+\frac{1}{13}-\frac{1}{19}+\frac{1}{19}-\frac{1}{25}+\frac{1}{25}-\frac{1}{31}+\frac{1}{31}-\frac{1}{37}\right)\)
\(L=\frac{1}{6}.\left(1-\frac{1}{37}\right)\)
\(L=\frac{1}{6}.\frac{36}{37}\)
\(L=\frac{6}{37}\)
\(S=\frac{5^2}{1.6}+\frac{5^2}{6.11}+...+\frac{5^2}{26.31}\)
\(=5\left[\left(1-\frac{1}{6}\right)+\left(\frac{1}{6}-\frac{1}{11}\right)+...+\left(\frac{1}{26}-\frac{1}{31}\right)\right]\)
\(=5\left[1-\frac{1}{31}\right]\)
\(=5.\frac{30}{31}=\frac{150}{31}\)
\(L=\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+\frac{1}{775}+\frac{1}{1147}\)
\(L.6=\frac{6}{1.7}+\frac{6}{7.13}+\frac{6}{13.19}+\frac{6}{19.25}+\frac{6}{25.31}\)
\(L.6=\left(1-\frac{1}{7}\right)+\left(\frac{1}{7}-\frac{1}{13}\right)+\left(\frac{1}{13}-\frac{1}{19}\right)+\left(\frac{1}{19}-\frac{1}{25}\right)+\left(\frac{1}{25}-\frac{1}{31}\right)\)
\(L.6=1-\frac{1}{31}\)
\(L.6=\frac{31}{31}-\frac{1}{31}\)
\(L.6=\frac{25}{31}\)
\(L=\frac{30}{31}:6\)
\(L=\frac{30}{31}.\frac{1}{6}\)
\(L=\frac{30}{186}\)
\(\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+\frac{1}{475}+\frac{1}{775}+\frac{1}{1147}\)
\(=\frac{1}{1\cdot7}+\frac{1}{7\cdot13}+\frac{1}{13\cdot19}+...+\frac{1}{31\cdot37}\)
\(=\frac{1}{6}\left(\frac{6}{1\cdot7}+\frac{6}{7\cdot13}+\frac{6}{13\cdot19}+...+\frac{6}{31\cdot37}\right)\)
\(=\frac{1}{6}\left(1-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+\frac{1}{13}-\frac{1}{19}+...-\frac{1}{31}-\frac{1}{37}\right)\)
\(=\frac{1}{6}\left(1-\frac{1}{37}\right)\)
\(=\frac{1}{6}\cdot\frac{36}{37}=\frac{6}{37}\)
Tổng cần tính bằng:\(\frac{1}{1.7}\)+\(\frac{1}{7.13}\)+\(\frac{1}{13.19}\)+\(\frac{1}{19.25}\)+\(\frac{1}{25.31}\)+\(\frac{1}{31.37}\)=(\(\frac{1}{1}\)-\(\frac{1}{7}\)+\(\frac{1}{7}\)-\(\frac{1}{13}\)+...+\(\frac{1}{31}\)\(\frac{1}{37}\)):3 =(\(1\)-\(\frac{1}{37}\)):3=\(\frac{12}{37}\)