Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
A= 7/5*7 + 7/7*9 + ... + 7/53*55
A= 7/2*( 2/5*7 + 2/7*9 + ... + 2/53*55 )
A= 7/2*( 7-5/5*7 + 9-7/7*9 + ... + 55-53/53*55 )
A= 7/2*( 1/5-1/7 + 1/7-1/9 + ... + 1/53-1/55 )
A= 7/2*( 1/5-1/55 )
A= 7/2*2/11
A= 7/11
A= 7/11 > 1/2
Nên: A > 1/2
B= 1/3 + 1/15 + 1/35 + ... + 1/99
B= 1/1*3 + 1/3*5 + 1/5*7 + ... + 1/9*11
B= 2*( 2/1*3 + 2/3*5 + 1/5*7 + ... + 2/9*11 )
B= 2*( 3-1/1*3 + 5-3/3*5 + 7-5/5*7 + ... + 11-9/9*11 )
B= 2*( 1/1-1/3 + 1/3-1/5 + 1/5-1/7 + ... + 1/9-1/11 )
B= 2*( 1/1-1/11 )
B= 2*10/11
B= 20/11
B= 20/11 < 1/2
Nên: B < 1/2
A= 7/5*7 + 7/7*9 + ... + 7/53*55
A= 7/2*( 2/5*7 + 2/7*9 + ... + 2/53*55 )
A= 7/2*( 7-5/5*7 + 9-7/7*9 + ... + 55-53/53*55 )
A= 7/2*( 1/5-1/7 + 1/7-1/9 + ... + 1/53-1/55 )
A= 7/2*( 1/5-1/55 )
A= 7/2*2/11
A= 7/11
A= 7/11 > 1/2
Nên: A > 1/2
B= 1/3 + 1/15 + 1/35 + ... + 1/99
B= 1/1*3 + 1/3*5 + 1/5*7 + ... + 1/9*11
B= 2*( 2/1*3 + 2/3*5 + 1/5*7 + ... + 2/9*11 )
B= 2*( 3-1/1*3 + 5-3/3*5 + 7-5/5*7 + ... + 11-9/9*11 )
B= 2*( 1/1-1/3 + 1/3-1/5 + 1/5-1/7 + ... + 1/9-1/11 )
B= 2*( 1/1-1/11 )
B= 2*10/11
B= 20/11
B= 20/11 < 1/2
Nên: B < 1/2
a,(11/15+4/15)+(5/7+2/7)
=1+1
=2
b,5/9x(1/2+6/4)
=5/9x2
=10/9
c,1/2:(7/8+9/8)
=1/2:2
=1
d,(17/10-7/10)+1/2
=1+1/2
=3/2
a) \(\frac{11}{15}+\frac{5}{7}+\frac{2}{7}+\frac{4}{15}=\left(\frac{11}{15}+\frac{4}{15}\right)+\left(\frac{5}{7}+\frac{2}{7}\right)\)
\(=2\)
b) \(\frac{5}{9}\times\frac{1}{2}\times\frac{5}{9}\times\frac{6}{4}=\frac{25}{81}\times\frac{3}{4}=\frac{25}{108}\)
c) \(\frac{7}{8}\div\frac{1}{2}+\frac{9}{8}\div\frac{1}{2}=\left(\frac{7}{8}+\frac{9}{8}\right)\div\frac{1}{2}\)
\(=2\div\frac{1}{2}=4\)
d) \(\frac{17}{10}+\frac{1}{2}-\frac{7}{10}=\left(\frac{17}{10}-\frac{7}{10}\right)+\frac{1}{2}\)
\(=1+\frac{1}{2}=\frac{3}{2}\)
a) \(\frac{11}{15}+\frac{5}{7}+\frac{2}{7}+\frac{4}{15}\)
\(=\left(\frac{11}{15}+\frac{4}{15}\right)+\left(\frac{5}{7}+\frac{2}{7}\right)\)
\(=1+1\)
\(=2\)
b) \(\frac{5}{9}.\frac{1}{2}.\frac{5}{9}.\frac{6}{4}\)
\(=\left(\frac{5}{9}\right)^2\left(\frac{1}{2}.\frac{6}{4}\right)\)
\(=\frac{25}{81}.\frac{3}{4}\)
\(=\frac{25}{108}\)
c) \(\frac{7}{8}:\frac{1}{2}+\frac{9}{8}:\frac{1}{2}\)
\(=\frac{7}{8}.2+\frac{9}{8}.2\)
\(=2\left(\frac{7}{8}+\frac{9}{8}\right)\)
\(=2.\frac{16}{8}\)
\(=2.2\)
\(=4\)
d) \(\frac{17}{10}+\frac{1}{2}-\frac{7}{10}\)
\(=\left(\frac{17}{10}-\frac{7}{10}\right)+\frac{1}{2}\)
\(=1+\frac{1}{2}\)
\(=\frac{2}{2}+\frac{1}{2}\)
\(=\frac{3}{2}\)
a)\(\frac{13}{15}+\frac{13}{35}+\frac{13}{63}+\frac{13}{99}\)
\(=\frac{13}{3.5}+\frac{13}{5.7}+\frac{13}{7.9}+\frac{13}{9.11}\)
\(=\frac{13}{2}\left(\frac{1}{3}-\frac{1}{5}+.....+\frac{1}{9}-\frac{1}{11}\right)\)
\(=\frac{13}{2}\left(\frac{1}{3}-\frac{1}{11}\right)\)
\(=\frac{13}{2}\cdot\frac{8}{33}\)
\(=\frac{52}{33}\)
a) Đặt A= 13/15 + 13/35 + 13/63 + 13/99
A = 13/2 ( 2/15 + 2/35 + 2/63 + 2/99)
A= 13/2 ( 2/ 3.5 + 2/5.7 + 2/7.9 + 2/9.11)
A= 13/2 ( 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11)
A= 13/2 ( 1/3 - 1/11)
A= 13/2 . 8/33
A= 52/33
A=1.078688093