Question

                                                                Tính các tổng sau:

A = 1.2+3.4+5.6 .... +99.100

B = 1.2²+2.3²+3.4²+....+99.100²

Answer 1

kho lam ai lam duoc

Answer 2

B = 1.2.2 + 2.3.3 + ....+ 99.100.100

=1.2.(3-1) + 2.3.(4-1)+ ....+99.100.(101-1)

=1.2.3 + 2.3.4 + .... + 99.100.101) - (2.3 + 3.4+.....+99.100)

Dối với bieu thuc thu nhat ban nhan ca tog cho 4 =) dc tong 98.99.100.101,bieu thuc thu hai ban nhan voi 3=)tong 98.99.100 roi tru di hai tong nay la xong.Con cau b minh ko biet

 

 

Answer 3

Giải:

A=

A=1.2.(3-1)+2.3.(4-1)+3.4.(5-1)+...+99.100.(101-1)

A=1.2.3-1.1.2+2.3.4-1.2.3+3.4.5-1.3.4+...+99.100.101-1.99.100

A=(1.2.3+2.3.4+4.5.6+...+99.100.101)-(1.2+2.3+3.4+...+99.100)

Gọi B=1.2.3+2.3.4+4.5.6+...+99.100.101

4B=1.2.3.(4-0)+2.3.4.(5-1)+...+(99.100.101(102-98)

4B=1.2.3.4+2.3.4.5-1.2.3.4+...+99.100.101.102-98.99.100.101

4B=99.100.101.102

4B=101989800

  B=25497450

Gọi C=1.2+2.3+3.4+...+99.100

3C=1.2.(3-0)+2.3.(4-1)+...+99.100.(101-98)

3C=1.2.3+2.3.4-1.2.3+...+99.100.101-98.99.100

3C=99.100.101

3C=999900

  C=999900:3

  C=333300

Vậy: A= 25497450 – 333300 =25164150

Answer 4

Đó là câu b đó bạn!

Answer 5

A = 1.2 + 3.4 + 5.6 + ... + 99.100

A.3 = 1.2.3 + 3.4.3 + 5.6.3 + ... + 99.100.3 

A.3 = 1.2.3 + 3.4.5 + 5.6.7 + ... + 99.100.101

A = 99.100.101 : 3 

A = 999900 : 3 

= 333300 

Answer 6

3A = 1.2.3 + 2.3.3 + 3.4.3 + … + 99.100.3
= 1.2.3 + 2.3.(4 - 1) + 3.4.(5 - 2) + … + 99.100. (101 - 98)
= 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + … + 99.100.101 - 98.99.100
= 99.100.101
A = 33.100.101 = 333 300

Answer 7

haizzzzzz khó quá

Answer 8

A=....

=>A=1.2+2.2.3+2.3.5+2.4.7+...+99.50.2

=>3A.3=1.1.2.(3.0)+2.2.3.(4-1)+2.3.5.(6-3)+...+50.2.99.(100-97)

=>3a=1.2.3+2.3.4-1.2.3+2.3.4-