\(A=1.3+3.5+5.7+...+97.99\)

\(\Rightarrow6A=1.3.6+3.5.\left(7-1\right)+5.7.\left(9-3\right)+...+97+99.\left(101-95\right)\)

\(\Rightarrow6A=1.3.6+3.5.7-1.3.5+5.7.9-3.5.7+...+97.99.101-95.97.99\)

\(\Rightarrow6A=1.3.6+97.99.101-1.3.5\)

\(\Rightarrow6A=3.\left(1+97.33.101\right)\)

\(\Rightarrow2A=1+323301\)

\(\Rightarrow2A=323302\)

\(\Rightarrow A=161651\)

D= 1 x 99 x 36 cặp = 3564

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 !


 

=3.(3/1.3+3/3.5+3/5.7+...+3/95.97+3/97.99)

=3(1-1/3+1/3-1/5+1/5-1/7+...+1/95-1/97+1/97-1/99)

=3[(1-1/99)+(1/5-1/5)+(1/7-1/7)+...+(1/97-1/97)]

=3(1-1/99)=3(99/99-1/99)=3.98/99=1.98/33=98/33

Neu la 3 ma ko phai la 3^2 thi sao : Tinh gium minh nha .