A = 1.2.3 + 2.3.4 + ... + 20.21.22
⇒ 4A = 1.2.3.4 + 2.3.4.4 + ... + 20.21.22.4
= 1.2.3.4 + 2.3.4.(5 - 1) + 3.4.5.(6 - 2) ... + 20.21.22.(23 - 19)
= 1.2.3.4 - 1.2.3.4 + 2.3.4.5 - 2.3.4.5 + 3.4.5.6 + ... - 19.20.21.22 + 20.21.22.23
= 20.21.22.23
= 212520
⇒ A = 212520 : 4 = 53130
S1 = __3__+__3__+...+__3__
1x2 2x3 99x100
S2=1+_1_ +_1_+_1_+...+_1_+_1_
2 4 8 2048 4096
S3=__1__+__1__+...+__1__
11x13 13x15 97x99
S4=1x2x3+2x3x4+3x4x5+...+20x21x22
S5__1__+__1__+__1__+...__1__
1x2x3 2x3x4 3x4x5 19x20x21
LÀM ƠN GHI GIÚP MÌNH CÁCH GIẢI NHÉ
Tính S=2/1x2x3+2/2x3x4+...+37x38x39
Giúp mk với. Mk cần gấp
C=1x2x3+2x3x4+...+48x49x50
giải nhanh giúp mik vs
Tính tổng;
A=1x2x3+2x3x4+...+7x8x9+8x9x10
giúp mk vs mk cảm ơn
A=1x2x3+2x3x4+3x4x5+...+99.100.101
Tính A biết A=1x2x3+2x3x4+...............+100x101x102
A=64+151+136+49;B=1x2x3+2x3x4+3x4x5+...+48x49x50
tính tổng sau :
A=1x2x3+2x3x4+3x4x5+..............+99x100x101.
A=1/1x2x3 +1/2x3x4 + .......+ 1/2014x2015x2016
