câu b nha

B= 1/100 - (1/2.1 + 1/3.2 + ... + 1/98.97 + 1/99.98 + 1/100.99)

B=1/100 - (1 - 1/2 + 1/2 - 1/3 + 1/3 - ... - 1/99 + 1/99 - 1/100)

B=1/100-(1-1/100)

B=1/100-99/100

B= - 98/100

B= - 49/50

đ ú g nha

- Câu a ~> http://olm.vn/hoi-dap/question/183158.html

A=\(\frac{-9}{16}\)

B= -1

Chắc bạn gõ nhầm số hạng thứ 3 phải là +5/7.

Tổng này đối xứng qua 13/15. Các đối xứng trái dấu nên Tổng = 13/15

Tính theo công thức nha bạn

\(B=\frac{1}{5}-\frac{3}{7}+\frac{5}{9}-\frac{2}{11}+\frac{7}{13}-\frac{9}{16}-\frac{7}{13}+\frac{2}{12}-\frac{5}{9}+\frac{3}{7}-\frac{1}{5}-\frac{1}{5}\)

\(B=\left(\frac{1}{5}-\frac{1}{5}\right)-\left(\frac{3}{7}-\frac{3}{7}\right)+\left(\frac{5}{9}-\frac{5}{9}\right)+\left(\frac{7}{13}-\frac{7}{13}\right)-\frac{2}{11}+\frac{2}{12}-\frac{9}{16}-\frac{1}{5}\)

\(B=0-0+0+0-\frac{2}{11}+\frac{2}{12}-\frac{9}{16}-\frac{1}{5}\)

\(B=\frac{-2}{11}+\frac{2}{12}-\frac{9}{16}-\frac{1}{5}\)

Đến đây chỉ còn cách quy đồng thôi

\(=\left(\frac{1}{5}-\frac{1}{5}\right)+\left(\frac{3}{7}-\frac{3}{7}\right)+\left(\frac{5}{9}-\frac{5}{9}\right)+\left(\frac{2}{11}-\frac{2}{11}\right)+\left(\frac{7}{13}-\frac{7}{13}\right)+\frac{9}{16}\)

= 0 + \(\frac{9}{16}\)

= \(\frac{9}{16}\)

tick nha bn

\(B=\frac{1}{5}-\frac{3}{7}+\frac{5}{9}-\frac{2}{11}+\frac{7}{13}-\frac{9}{16}-\frac{7}{13}+\frac{2}{11}-\frac{5}{9}+\frac{3}{7}-\frac{1}{5}\)

    \(=\left(\frac{1}{5}-\frac{1}{5}\right)+\left(-\frac{3}{7}+\frac{3}{7}\right)+\left(\frac{5}{9}-\frac{5}{9}\right)+\left(-\frac{2}{11}+\frac{2}{11}\right)+\left(\frac{7}{13}-\frac{7}{13}\right)-\frac{9}{16}\)

    \(=0+0+0+0+0-\frac{9}{16}\)

    \(=-\frac{9}{16}\)

 ^...^  ^_^

cái này đăng hôm qua đến giờ 5 lần rồi,4 câu kia tui làm rồi vô chtt kiém coi có hk

B=(1/5-1/5) + (-3/7+3/7) + (5/9-5/9) + (-2/11+2/11) + (7/13-7/13) - 9/16

  =     0       +       0       +      0      +         0         +      0         -  9/16

  =-9/16

bằng -9/16

B = 1 /5*(-3) /7 + 5 /9*(-2) /11 + 7 /13*(-9) /16*(-7) /13 + 2 /11*(-5) /9 + 3 /7*(-1) /5

B=-9/16

http://coccoc.com/search#query=T%C3%ADnh+nhanh+++B%3D+1%2F+5+%E2%88%92+3%2F+7+%2B+5%2F+9+%E2%88%92+2+%2F11+%2B+7%2F+13+%E2%88%92+9%2F+16+%E2%88%92+7+%2F13+%2B+2%2F+11+%E2%88%92+5%2F+9+%2B+3+%2F7+%E2%88%92+1%2F+5+

Ok

\(B=\left(\frac{1}{5}-\frac{1}{5}\right)+\left(-\frac{3}{7}+\frac{3}{7}\right)+\left(\frac{5}{9}-\frac{5}{9}\right)+\left(-\frac{2}{11}+\frac{2}{11}\right)+\left(\frac{7}{13}-\frac{7}{13}\right)-\frac{9}{16}\)

\(B=0+0+0+0+0+\left(-\frac{9}{16}\right)=-\frac{9}{16}\)

\(B=\frac{1}{5}-\frac{3}{7}+\frac{5}{9}-\frac{2}{11}+\frac{7}{13}-\frac{9}{16}-\frac{7}{13}+\frac{2}{11}-\frac{5}{9}+\frac{7}{3}-\frac{1}{5}\)
\(B=\left(\frac{1}{5}-\frac{1}{5}\right)+\left(\frac{3}{7}-\frac{3}{7}\right)+\left(\frac{5}{9}-\frac{5}{9}\right)+\left(\frac{2}{11}-\frac{2}{11}\right)+\left(\frac{7}{11}-\frac{7}{11}\right)-\frac{9}{16}\)
\(B=0+0+0+0+0-\frac{9}{16}=-\frac{9}{16}\)

A= 1/3- 3/4+ 3/5+ 1/72- 2/9- 1/36+ 1/15
A= ( 1/3- 3/5+ 1/15) - (3/4- 1/72+ 2/9+ 1/36)
A= (5/15- 9/15+ 1/15) - (54/72- 1/72+ 16/72+ 2/36)
A= 1- 71/72
A= 1/72
 
 

A=1/72

A = \(\frac{1}{3}\)- \(\frac{3}{4}\) - ( - \(\frac{3}{5}\)) + \(\frac{1}{72}\)- \(\frac{2}{9}\)- \(\frac{1}{36}\)+ \(\frac{1}{15}\)

A =   (  \(\frac{1}{3}\)+ \(\frac{3}{5}\)+ \(\frac{1}{15}\)) -  ( \(\frac{3}{4}\)- \(\frac{1}{72}\)+ \(\frac{2}{9}\)+ \(\frac{1}{36}\))

A =    ( \(\frac{5}{15}\)+ \(\frac{9}{15}\)+ \(\frac{1}{15}\)) - ( \(\frac{54}{72}\)- \(\frac{1}{72}\)+ \(\frac{16}{72}\)+ \(\frac{2}{72}\))

A =          1               -            \(\frac{71}{72}\)

A =                  \(\frac{1}{72}\)