Đặt tổng trên là A

Có : 3A = 1.2.3+2.3.3+....+n.(n+1).3

= 1.2.3+2.3.(4-1)+......+n.(n+1).[(n+2)-(n-1)]

= 1.2.3+2.3.4-1.2.3+.....+n.(n+1).(n+2)-(n-1).n.(n+1)

= n.(n+1).(n+2)

=> A = n.(n+1).(n+2)/3

Tk mk nha

Đặt A=1.2+2.3+...+n(n+1)

3A=1.2.3+2.3.3+...+n(n+1).3

3A=1.2.(3-0)+2.3.(4-1)+...+n(n+1)[(n+2)-(n-1)]

3A=1.2.3-0.1.2+2.3.4-1.2.3+...+n(n+1)(n+2)-(n-1)n(n+1)

3A=[1.2.3+2.3.4+...+n(n+1)(n+2)]-[0.1.2+1.2.3+...+(n-1)n(n+1)]

3A=n(n+1)(n+2)-0.1.2

3A=n(n+1)(n+2)

A=\(\frac{n\left(n+1\right)\left(n+2\right)}{3}\)

Ta có : S = 1.2 + 2.3 + 3.4 + ..... + 32.33

=> 3S = 1.2.3 - 1.2.3 + 2.3.4 - 2.3.4 + ...... + 32.33.34

=> 3S = 32.33.34

=> S = \(\frac{32.33.34}{3}=11968\)

A=1.2+2.3+...+49.50

3A=1.2.3+2.3.3+...+49.50.3

3A=1.2.(4-1)+2.3.(5-2)+....+49.50.(51-48)

3A=1.2.4-1.2.1+2.3.5-2.3.2+...+49.50.51-49.50.48

3A=49.50.51

=>A=49.25.51

=>A=62475

A=1.2+2.3+...+49.50

3A=1.2.3+2.3.3+...+49.50.3

3A=1.2.(4-1)+2.3.(5-2)+....+49.50.(51-48)

3A=1.2.4-1.2.1+2.3.5-2.3.2+...+49.50.51-49.50.48

3A=49.50.51

=>A=49.25.51

=>A=62475

3S=(1.2+2.3+3.4+...+49.50).3

3S=1.2.3+2.3.3+3.4.3+...+49.50.3

3S=1.2.3+2.3.(4-1)+3.4.(5-2)+...+49.50.(51-48)

3S=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+49.50.51-48.49.50

3S=49.50.51

S=17.49.50

41650 tk m nhé

Nhân cả 2 vế của S với 3 ta được :

3S = 3(1.2 + 2.3 + 3.4 + ..... + 49.50)

= 1.2.3 + 2.3.3 + 3.4.3 + ... + 49.50.3

= 1.2.3 + 2.3.(4 - 1) + 3.4.(5 - 2) + .... + 49.50.(51 - 48)

= 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + .... + 49.50.51 - 48.59.50

= (1.2.3 - 1.2.3) + (2.3.4 - 2.3.4) + ......... + (48.49.50 - 48.49.50) + 49.50.51

= 49.50.51

=> S = 49.50.51/3 = 41650

Ta có: 3S=1.2.3+2.3.(4-1)+3.4.(5-2)+...+49.50(51-48)

=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+....+49.50.51-48.49.50

=49.50.51

=124950

\(A=\frac{9}{1.2}+\frac{9}{2.3}+\frac{9}{3.4}+...+\frac{9}{98.99}+\frac{9}{99.100}\)

\(A=\frac{1}{9}.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{98.99}+\frac{1}{99.100}\right)\)

\(A=\frac{1}{9}.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\right)\)

\(A=\frac{1}{9}.\left(1-\frac{1}{100}\right)\)

\(A=\frac{1}{9}.\frac{99}{100}\)

\(A=\frac{11}{100}\)

A = 9/1.2 + 9/2.3 + 9/3.4 +...+ 9/98.99 + 9/99.100

   = 9. (1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/98 - 1/99 + 1/99 - 1/100)

   = 9. (1 - 1/100)

   = 9 . 99/100

   = 891/100

a) Đ

b) S

Vì tổng của hai số nguyên bằng 0 thì cả hai số nguyên đó đều bằng 0 hoặc hai số đó là hai số đối nhau. Ví dụ: (-3) + 3 = 0+ 0 = 0

c) Đ

d) S

Vì khẳng định sẽ bị sai khi các số nguyên đó không cùng dấu.

3.s =1.2.3+2.3.3 +3.4.3+........+49.50

3s= 1.2 .3+ 2.3.(4-1) +.....+ 49.50( 51-48)

3s=49.50.51

3s=124950

s= 124950chia 3

s= 41650

chia=/ or chia= :

\(Dear,Ph\text{ạm}Nguy\text{ễn}H\text{à}Vi \)z=312579 21yiauy9-6 m4n 8bv38 vfffffffffffffffffduvfeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeesjk8bxhcngtrfhftoxd9 rn r r r r r xcvnoiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiim89;pllllhj54rtxc rdt76nb5cvrt88888f9 r5fc7y p88;g bạn giỏi quá

3S=1.2.3+2.3.3+3.4.3+...+49.50.3
=1.2.3+2.3.(4-1)+3.4.(5-2)+...+48.49.(50-47)+49.50.(51-48)
=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+48.49.50-47.48.49+49.50.51-48.49.50
=(1.2.3-1.2.3)+(2.3.4-2.3.4)+...(47.48.49-47.48.49)-(48.49.50-48.49.50)+49.50.51
=0+0+...+0+0+49.50.51
=49.50.51
S=(49.50.51)/3
=41650
Đáp số:41650

lê thị ngọc anh trả lời đúng đấy tin bạn ấy đi

3S=1.2.3+2.3.3+3.4.3+...+49.50.3

=1.2.3+2.3.(4-1)+3.4.(5-2)+...+48.49.(50-47)+49.50.(51-48)

=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+48.49.50-47.48.49+49.50.51-48.49.50

=(1.2.3-1.2.3)+(2.3.4-2.3.4)+...(47.48.49-47.48.49)-(48.49.50-48.49.50)+49.50.51

=0+0+...+0+0+49.50.51

=49.50.51

S=(49.50.51)/3

=41650