Đặt A = 1.2+2.3+3.4+....+98+99
ð 3a = 1.2.3-1.2.3+2.3.4+...+98.99.100
ð 3a=98.99.100
ð A=98.99.100/3
ð A=323400
Đặt A = 1.2 + 2.3 + 3.4 + ...... + 98.99
=> 3A = 1.2.3 - 1.2.3 + 2.3.4 - 2.3.4 + ....... + 98.99.100
=> 3A = 98 .99.100
=> A = 98 .99.100/3
=> A = 323400
Đặt A = 1.2+2.3+3.4+....+98+99
ð 3a = 1.2.3-1.2.3+2.3.4+...+98.99.100
ð 3a=98.99.100
ð A=98.99.100/3
ð A=323400
Đặt A = 1.2+2.3+3.4+....+98+99
ð 3a = 1.2.3-1.2.3+2.3.4+...+98.99.100
ð 3a=98.99.100
ð A=98.99.100/3
ð A=323400
Đặt A = 1.2+2.3+3.4+....+98+99
ð 3a = 1.2.3-1.2.3+2.3.4+...+98.99.100
ð 3a=98.99.100
ð A=98.99.100/3
ð A=323400
Đặt A vào biểu thức, ta có:
A = 1.2+2.3+3.4+4.5+5.6+...+98.99
3A = 1.2.3 + 2.3.3+ 3.4.3 + .... + 99 . 100 . 3
3A = 1.2.3 + 2 . 3 . ( 4 - 1 ) + 3.4 . ( 5 - 2 ) + ....+ 99 . 100 . ( 101 - 98 )
3A = 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 - 2.3.4 + ...+ 99 .100.101 - 98. 99 . 100
3A = ( 1.2.3 - 1.2.3 ) + ( 2.3.4 - 2.3.4 ) + ...+ ( 98 .99 .100 - 98 . 999 .100 ) + 99 .100 . 101
3A = 99 . 100 . 101
3A = 999900
A = 999900 : 3
A = 333300
^^ Học tốt nhé!
Đặt A = 1.2+2.3+3.4+....+98+99
ð 3a = 1.2.3-1.2.3+2.3.4+...+98.99.100
ð 3a=98.99.100
ð A=98.99.100/3
ð A=323400
Đặt A = 1.2+2.3+3.4+....+98+99
ð 3a = 1.2.3-1.2.3+2.3.4+...+98.99.100
ð 3a=98.99.100
ð A=98.99.100/3
ð A=323400
Songoku Sky Fc11 coppy mà đc tích thì cạn lời oi
Đặt A = 1.2+2.3+3.4+....+98+99
ð 3a = 1.2.3-1.2.3+2.3.4+...+98.99.100
ð 3a=98.99.100
ð A=98.99.100/3
ð A=323400
Đặt A = 1.2+2.3+3.4+....+98+99
ð 3a = 1.2.3-1.2.3+2.3.4+...+98.99.100
ð 3a=98.99.100
ð A=98.99.100/3
ð A=323400
Đặt A = 1.2+2.3+3.4+....+98.99
3a = 1.2.3-1.2.3+2.3.4+....+98.99.100
3a = 98.99.100
A = ( 98.99.100 ) ÷ 3
A = 323400