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

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

= 1.2.3 - 0 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + ... + 99.100.101 - 98.99.100

= 99.100.101

=> S = 99.100.101 / 3

=> S = 333300

ta có \(3S=1\cdot2\cdot3+2\cdot3\cdot3+.....+99\cdot100\cdot3\)

\(3S=1\cdot2\cdot3+2\cdot3\cdot\left(4-1\right)....+99\cdot100\cdot\left(101-98\right)\)

\(3S=1\cdot2\cdot3-1\cdot2\cdot3+2\cdot3\cdot4-......-98\cdot99\cdot100+99\cdot100\cdot101\)

\(3S=99.100.101\)

\(S=\frac{99\cdot100\cdot101}{3}\)

S=...

3S=1.2.3+2.3.3+3.4.3+4.5.3+...+99.100.3

3S=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+4.5.6-3.4.5+...+99.100.101-98.99.100

3S=99.100.101

S=33.100.101

S=333300

Vậy S=333300

( 99,1 - 1,2 ) : 1,1 + 1 = 90

S là :

( 99,1 + 1,2 ) x 90 : 2 = 4513,5

Đặt M = 1 . 2 + 2 . 3 + ... + 99 . 100 

3M = 1 . 2 . 3 + 2 . 3 . 4 + 3 . 4 . 3 + ... + 99 . 100 . 3

3M = 1 . 2 . ( 3 - 0 ) + 2 . 3 . ( 4 - 1 ) + 3 . 4 . ( 5 - 2 ) ... . 99 . 100 . ( 101 - 98 ) 

3M = ( 1 . 2 . 3 + 2 . 3 . 4 + 3 . 4 . 5 +... + 99 . 100 . 101 ) - ( 0 . 1 . 2 + 1 . 2 . 3 + 2 . 3 . 4 +.......+ 98 . 99 . 100 )

3M = 99 . 100 . 101 - 0 . 1 . 2 

3M = 999900 - 0 = 999900

M = 999900 : 3

M  = 333300

ban oi giai cach khac cach nay minh roi

Đặt A = 1 . 2 + 2 . 3 + 3 . 4 + ... + 99 . 100

3 . A  = 1 . 2 . 3 + 2 . 3 . 3 + 3 . 4 . 3 + ... + 99 . 100 . 3

3 . A = 1 . 2 . 3 + 2 . 3 . ( 4 - 1 ) + 3 . 4 . ( 5 - 2 ) + ... + 99 . 100 . ( 101 - 98 ) 

3 . A =  ( 1 . 2 . 3 + 2 . 3 . 4 + 3 . 4 . 5 + ... + 99 . 100 . 101 ) - ( 0 . 1 . 2 + 1 . 2 . 3 + 2 . 3 . 4 + ... + 98 . 99 . 100 )

3 . A = 99 . 100 . 101 - 0 . 1 . 2 

3 . A = 999900 - 0

3 . A = 999900

A = 999900 : 3 

A = 333300

Vậy 1 . 2 + 2 . 3 + 3 . 4 + ... + 99 .100 = 333300

1) (x-3)(x-5) = 0

\(\Rightarrow\orbr{\begin{cases}x-3=0\\x-5=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=3\\x=5\end{cases}}\)

(x+7).35 = 2.35

\(\Rightarrow x+7=2\)

\(\Rightarrow x=2-7=-5\)

Vậy x = -5

2) 1.2 + 2.3 + 3.4 + .... + 99.100

Đặt A = 1.2 + 2.3 + .... + 99.100

3A = 1.2.3 + 2.3.4 + 3.4.3 + .... + 99.100.3

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

3A = ( 1.2.3 + 2.3.4 + 3.4.5 +.... + 99.100.101 ) - ( 0.1.2 + 1.2.3 + 2.3.4 + ... + 98.99.100 )

3A = 99.100.101 - 0.1.2

3A = 999900 - 0

3A = 999900

A = 999900 : 3

A = 333300

Vậy A = 333300

1

\(\left(x-3\right)\left(x-5\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x-3=0\\x-5=0\end{cases}\Rightarrow\orbr{\begin{cases}x=-3\\x=-5\end{cases}}}\)

\(\left(x+7\right).35=2.35\)

\(x+7=2=>x=-5\)

A=1.2+2.3+3.4...+99.100
=> 3A= 1.2.3+2.3.3+3.4.3...+99.100.3
=> 3A=1.2.(3-0)+2.3.(4-1)+3.4.(5-2)+...+99.100(101=98)
=> 3A= (1.2.3+2.3.4+3.4.5+...+99.100.101)-(0.1.2+1.2.3+..+98.99.200)
=> 3A= 99.100.101-0.1.2
=> 3A= 999900-0=999900
=> A= 999900:3=333300

kết quả là 4513.5

ĐẶT A LÀM BIỂU THỨC 

=>A=1.2+2.3+3.4+.+99.100

=>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)

=>A=1.2.3+2.3.4-1.2.3-3.4.5-2.3.4+.....+98.99.100-99.100.101

=>A3=99.100.101

=>A=99.100.101:3

=>A=333300

tk đi rồi mk làm cho bài này quá dễ

Đặt A = 1.2 + 2.3 + 3.4 + .... + 99.100

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

\(\Rightarrow A=\frac{99.100.101}{3}=333300\)

Đặt A = 1.2 + 2.3 + 3.4 + ... + 99.100

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 + 3.4.5 + .... + 99.100.101 ) - ( 0.1.2 + 1.2.3 + 2.3.4 + ....+ 98.99.100 )

3A = 99.100.101 - 0.1.2

3A = 999900 - 0 

3A = 999900

  A = 999900 : 3

  A = 333300

ĐẶT A=1.2+2.3+3.4+..+99.100

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+2.3.4-2.3.1+.....+98.99.100-99.100.101

3A=99.100.101

A=33300

Đặt A = 1.2+2.3+3.4+........+99.100

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

 => 3A = 1.2.3 - 1.2.3 + 2.3.4 - 2.3.4 + ..... + 99.100.101

 => 3A = 99.100.101

 => A = 99.100.101/3

  => A = 333300      

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

3A = 1.2.3 - 0.1.2 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + ... + 99.100.101 - 98.99.100

3A = 99.100.101 - 0.1.2

3A = 99.100.101

A = 33.100.101

A = 333300

\(B=1.2+2.3+3.4+4.5+....+99.100\)

\(3B=1.2.3+2.3.\left(4-1\right)+3.4.\left(5-2\right)+...+99.100.\left(101-98\right)\)

\(3B=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+....+99.100.101-98.99.100\)

\(3B=99.100.101\)

\(B=\frac{99.100.101}{3}=\frac{999900}{3}=333300\)

3B LA GI HA BAN