= 1-1/3 + 1/3-1/5+.......+1/97-1/99

=  1 - 1/99

= 98/99

sao lại là 1- 1/3 + 1/3 -1/5 + ...... 1/97 - 1/99 hả bạn :|

\(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+.....+\frac{2}{95.97}\)\(+\frac{2}{97.99}\)

\(=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-....-\frac{1}{97}+\frac{1}{97}-\frac{1}{99}\)

\(=1-\frac{1}{99}\)

\(=\frac{98}{99}\)

B=3×53​+5×73​+7×93​+...+48×503​ 

\(B = \frac{3}{2} \times \left(\right. \frac{2}{3 \times 5} + \frac{2}{5 \times 7} + \frac{2}{7 \times 9} + . . . + \frac{2}{48 \times 50} \left.\right)\) 

\(B = \frac{3}{2} \times \left(\right. \frac{1}{3} - \frac{1}{5} + \frac{1}{5} - \frac{1}{7} + \frac{1}{7} - \frac{1}{9} + . . . + \frac{1}{48} - \frac{1}{50} \left.\right)\) 

\(B = \frac{3}{2} \times \left(\right. \frac{1}{3} - \frac{1}{50} \left.\right)\)

\(B = \frac{3}{2} \times \frac{47}{150}\) 

\(B = \frac{47}{100}\) 

Dấu :  \("."\)là dấu nhân nhé 

\(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{77.79}\)

\(=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{77}-\frac{1}{79}\)

\(=1-\frac{1}{79}\)

\(=\frac{79}{79}-\frac{1}{79}\)

\(=\frac{78}{79}\)

Chúc bạn học tốt !!! 

Giá trị biểu thức là 78/79

mình cảm ơn bạn

Đặt biểu thức = A

6A = 1x3x6 + 3x5x6+....+ 97x99x6

= 1x3x(1+5) + 3x5x(7-1) + 5x7x(9-3) +.....+ 97x99x(101-95)

= 1x3+1x3x5+3x5x7-1x3x5+5x7x9-3x5x7+.....+97x99x101-95x97x99

= 1x3+97x99x101

= 969906

=> A = 161651

k mk nha