\(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{97.99}\)

\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{97}-\frac{1}{99}\)

\(=\frac{1}{3}+\left(\frac{1}{5}-\frac{1}{5}\right)+\left(\frac{1}{7}-\frac{1}{7}\right)+...+\left(\frac{1}{97}-\frac{1}{97}\right)-\frac{1}{99}\)

\(=\frac{1}{3}-\frac{1}{99}=\frac{32}{99}\)

~ Hok tốt ~

\(\)

Viết thành 2 . (1/3.5 + 1/5.7 + 1/7.9 + ...+ 1/97.99

Tui hk bít nữa

S=1.3+3.5+5.7+....+97.99

S=(1+3+5+7+......+97).(3+5+7+........+99)

S=1+99+(3+5+7+......+97).2

S= 1+99+2400                  .2

S=1+99+ 4800

S=100+4800

S=4900

Nhớ tick cho mình nha

Kết quả là:

 161651

  Đpá số: 161651

161651

ban nhe

tk nha@@@@@@@@@@@@@@@@@@@@@@@@2

hihi

Bạn tham khảo :

https://h.vn/hoi-dap/question/122304.html

Hok tốt !

A = 1.3 +3.5 + 5.7 + ...+ 97.99

6A= 1.3.6 + 3.5.6 + 5.7.6 + ... + 97.99.6

    = 1.3.(5+1) + 3.5.(7-) + 5.7(9-3) + ... + 97.99(101-95)

   = 1.3.5 + 1.3 + 3.5.7 - 1.3.5 + 5.7.9 - 3.5.7 + ... + 97.99.101 - 95.97.99

   = 1.3.5 + 3 + 3.5.7 - 1.3.5 + 5.7.9 - 3.5.7 + .... + 97 .99.101 - 95.87.99

=3+97.99.101

=> A = ( 1+97.33.101) : 2

A= 161651

A = 1.3 + 3.5 + 5.7 + … + 97.99

6A = 1.3.6 + 3.5.6 + 5.7.6 + … + 97.99.6

     = 1.3.(5 + 1) + 3.5.(7 - 1) + 5.7(9 - 3) + … + 97.99(101 - 95)

     = 1.3.5 + 1.3 + 3.5.7 - 1.3.5 + 5.7.9 - 3.5.7 + … + 97.99.101 - 95.97.99

     = 1.3.5 + 3 + 3.5.7 - 1.3.5 + 5.7.9 - 3.5.7 + … + 97.99.101 - 95.97.99

      = 3 + 97.99.101

⇒ A = 1 + 97 . 99 . 101 /2 =  161651

Chúc bạn học tốt !


 

\(S=4\left(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{97}-\dfrac{1}{99}\right)\)

\(=4\cdot\left(\dfrac{1}{3}-\dfrac{1}{99}\right)=4\cdot\dfrac{32}{99}=\dfrac{128}{99}\)

=4⋅3299=12899















   
   

2/3.5+ 2 /5.7+ 2/7.9+...+ 2/97.99

=1/3-1/5+1/5-1/7+1/7-1/9+....+1/97-1/99

=1/3-1/99

=32/99

2/3.5 + 2/5.7 +...+ 2/97.99

=1/3 - 1/5 + 1/5 - 1/7 + ... + 1/97 - 1/99

=1/3 - 1/99

=32/99

= 2/ 3.5 = 1/3 - 1/5 ; 2/ 5.7 = 1/5 - 1/7 ;........; 2/ 97.99 = 1/97 - 1/99

= 1/3 - 1/99 = 32/99

\(\frac{2}{3\times5}+\frac{2}{5\times7}+.....+\frac{2}{97\times99}\)

\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+....+\frac{1}{97}-\frac{1}{99}\)

\(=\frac{1}{3}-\frac{1}{99}\)

\(=\frac{32}{99}\)

= \(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{97}-\dfrac{1}{99}\)

\(=\dfrac{1}{3}-\dfrac{1}{99}=\dfrac{32}{99}\)

= \(\dfrac{\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{97}-\dfrac{1}{99}}{2}\)

= \(\dfrac{\dfrac{1}{3}-\dfrac{1}{99}}{2}=\dfrac{16}{99}\)

Bài kia mk nhầm sorry