Question

(2+4+6+...+100) - (1+3+5+...+99) = ?

1 x 2 + 2 x 3 + 3 x 4 + ... + 99 x 100 = ?

3 x 4 + 4 x 5 + 5 x 6 + ... + 149 x 150 = ?

1 + (1 + 2) + ( 1 + 2 + 3) + (1 + 2 + 3 + 4) + ....... + (1 + 2 + 3 + ... + 99)

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1 x 99 + 2.98 + 3.97 + ...... + 99 x 1

Answer 1

không biết giải

Answer 2

2001 

____

1991

Answer 3

1/1*2+1/2*3+1/3*4+1/4*5+...1/99+100

Answer 4

Đặt S = 1*2 + 2*3 + 3*4 + ........+ 99*100

=> 3S = 1.2.3 + 2.3.3+3.4.3+...+99.100.3

=> 3S = 1.2.(3-0)+2.3.(4-1)+3.4.(5-2)+...+99.100.(101-98)

=> 3S = 1.2.3 - 0.1.2 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4+...+99.100.101 - 98.99.100

=> 3S = 99.100.101 = 999900

=>S = 333300 

Answer 5

Đặt S = 1*2 + 2*3 + 3*4 + ........+ 99*100

=> 3S = 1.2.3 + 2.3.3+3.4.3+...+99.100.3

=> 3S = 1.2.(3-0)+2.3.(4-1)+3.4.(5-2)+...+99.100.(101-98)

=> 3S = 1.2.3 - 0.1.2 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4+...+99.100.101 - 98.99.100

=> 3S = 99.100.101 = 999900

=>S = 333300 

Đảm bảo đúng!!!

  
 

Answer 6

56rtfrgfgfgf

Answer 7

333300