Biet lam ti tick tui 1 cai nha Trần Hải An

\(B=1.4+2.5+3.6+...+99.102=1\left(2+2\right)+2\left(3+2\right)+3\left(4+2\right)+...+99\left(100+2\right)\)

\(=1.2+1.2+2.3+2.2+3.4+3.2+...+99.100+99.2\)

\(=\left(1.2+2.3+3.4+...+99.100\right)+2.\left(1+2+3+...+99\right)\)

Tính \(E=1.2+2.3+3.4+...+99.100\)

\(\Rightarrow3E=1.2.\left(3-0\right)+2.3\left(4-1\right)+3.4\left(5-2\right)+...+99.100\left(101-98\right)\)\(=\left(1.2.3+2.3.4+3.4.5+...+99.100.101\right)-\left(1.2.3+2.3.4+3.4.5+...+98.99.100\right)\)

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

Tính \(F=2.\left(1+2+3+...+99\right)\)

\(=2.\left(\frac{\left(99+1\right)99}{2}\right)=100.99=9900\)

Vậy, \(B=E+F=333300+9900=343200\)

Giải chi mà dài vậy tui làm nhanh hơn nhiều nhớ chọn tui nha 

Ta áp dụng công thức 1.3+2.4+3.5+...+(n-1).(n+1)=n:6.[(n-1).(2n+1)]

Vậy bài toán này tui làm như sau: 1.4+2.5+3.6+....+99.102

=102:6.[(102-1).(102.2+1)]=17.[101.205]=17.20705=351985

1.4+2.5+3.6+...+99.102=1(2+2)+2(3+2)+3(4+2)+...99(100+2)

=1.2+1.2+2.3+2.2+...+99.100+99.2

=(1.2+2.3+...+99.100)+2(1+2+...+99)

A=1.2+2.3+3.4+...+99.100(cho A la ten bieu thuc nay)

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

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

=99.100.101=>A=\(\frac{99.100.101}{3}\)=33330

2.(1+2+...99)

=2(100.99:2)=2.4950=9900

33330+9900=343200

vay...

A = 1.4 + 2.5 + 3.6 + ... + 99.102

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

A = (1.2 + 2.3 + 3.4 + ... + 99.100) + (1.2 + 2.2 + 3.2 + ... + 99.2)

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

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

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

3B = 99.100.101

B = 33.100.101 = 333300

A = 333300 + 2.(1 + 2 + 3 + ... + 99)

A = 333300 + 2.(1 + 99).99:2

A = 333300 + 100.99

A = 333300 + 9900

A = 343200

 A = 1.4 + 2.5 + 3.6 +...+ 99.102

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

A = 1.2+1.2+2.3+2.2+3.4+3.2+.+99.100+99.2

A = (1.2+2.3+3.4+.+99.100)+2(1+2+3+.+99)

A = 1.4 + 2.5 + 3.6 + ... + 99.102
A = 1.(2 + 2) + 2.(3 + 2) + 3.(4 + 2) + ... + 99.(100 + 2)
A = (1.2 + 2.3 + 3.4 + ... + 99.100) + (1.2 + 2.2 + 3.2 + ... + 99.2)
Đặt B = 1.2 + 2.3 + 3.4 + ... + 99.100
3B = 1.2.(3-0) + 2.3.(4-1) + 3.4.(5-2) + ... + 99.100.(101-98)
3B = 1.2.3 - 0.1.2 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + ... + 99.100.101 - 98.99.100
3B = 99.100.101
B = 33.100.101 = 333300
A = 333300 + 2.(1 + 2 + 3 + ... + 99)
A = 333300 + 2.(1 + 99).99:2
A = 333300 + 100.99
A = 333300 + 9900
A = 343200

bn bùi phạm 2007  đúng rùi nha!

k mk nhé!

1.4+2.5+3.6+...+99.102

= 1( 2 + 2 ) + 2 ( 3 + 2 ) + 3 ( 4 + 2 ) + . . . +99 ( 100 + 2 )

= 1. 2 + 1. 2 + 2.3 + 2.2 + 3. 4 + 3.2 + . . . + 99.100 + 100 . 2

= ( 1.2 + 2.3 + 3.4 + . . . + 99.100) + 2 ( 1 + 3 + 5 + . . . + 99 )

= 333300  + 9900

= 343200

Tk mk nha

1.4 + 2.5 + 3.6 + ..... + 99.102

= 1.(2 + 2) + 2.(3 + 2) + 3.(4 + 2) + ..... + 99.(100 + 2)

= 1.2 + 2 + 2.3 + 2.2 + 3.4 + 2.3 + .... + 99.100 + 2.99

= (1.2 + 2.3 + 3.4 + .... + 99.100) + (1.2 + 2.2 + 3.2 + .... + 2.99)

= 333300 + 2[(99.100)/2]

= 343200

\(B=1.4+2.5+3.6+...+99.102\)

\(=1.\left(2+2\right)+2.\left(2+3\right)+3.\left(2+4\right)+...+99.\left(2+100\right)\)

\(=1.2+2.1+2.3+2.2+3.4+2.3+...+99.100+2.99\)

\(=\left(1.2+2.3+...+99.100\right)+\left(2.1+2.2+2.3+...+2.99\right)\)

\(=333300+2.\left(1+2+3+...+99\right)\)

\(=333300+2.\left(\frac{99.100}{2}\right)\)

\(=333300+99.100=333300+9900=343200\)

kb với mình nha

A = 1(2+2)+2(3+2)+3(4+2)+...+99(100+2) 
A = 1.2+1.2+2.3+2.2+3.4+3.2+...+99.100+99.2 
A = (1.2+2.3+3.4+...+99.100)+2(1+2+3+...+99) 

A = 333300 + 9900 = 343200 

CHÚC BẠN HỌC TỐT ^-^

=(102 - 1) +1 :3
= 34
(bạn lấy số cuối trừ số đầu cộng 1 chia khoảng cách là 3)

Cái này là toán lp 6 nha bn

A = 1.4 + 2.5 + 3.6 + ... + 99.102

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

A = 1.2 + 1.2 + 2.2 + 2.3 + 3.2 + 3.4 + ... + 99.2 + 99.100

A = (1.2 + 2.2 + 3.2 + ... + 99.2) + (1.2 + 2.3 + 3.4 + ... + 99.100)

A = 2.(1 + 2 + 3 + ... + 99) + 1/3.[1.2.(3-0) + 2.3.(4-1) + 3.4.(5-2) + ... + 99.100.(101-98)]

A = 2.(1 + 99).99:2 + 1/3.(1.2.3 - 0.1.2 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + ... + 99.100.101 - 98.99.100)

A = 100.99 + 1/3.99.100.101

A = 9900 + 33.100.101

A = 9900 + 333300

A = 343200

Ủng hộ mk nha ^_-