Đặt biểu thức là A
\(\Rightarrow3A=1.2.3+2.3.3+3.4.3+...+98.99.3\)
\(3A=1.2.3+2.3.\left(4-1\right)+3.4.\left(5-2\right)+...+98.99.\left(100-97\right)\)
\(3A=1.2.3-1.2.3+2.3.4-2.3.4+3.4.5-...-97.98.99+98.99.100\)
\(3A=98.99.100\Rightarrow A=98.33.100\)
Tinh: M =101+100+99+98+...+4+3+2+1/101-100+99-98+...-4+3-2+1
Viết lời giải luôn nhé
tinh: D= 1*2*3+2*3*4+3*4*5+...+98*99*100
tinh 1*99+2*98+3*97+....+98*2+99*1
tinh 1+2^2+3^2+4^2+...+98^2+99^2
4.tinh tong
1/ 1+(-2)+3+(-4)+...+19+(-20)
2/ 1-2+3-4+...+99-100
3/ 2-4+6-8+...+48-50
4/ -1+3-5+7-...+97-99
5/1+2-3-4+...+97+98-99-100
tinh tong
1+(-2)+3+(-4)+.....+19+(-20)1-2+3-4+.....+99-1002-4+6-8+......+48-50-1+3-5+7-....+97-991+2-3-4+......+97+98-99-100tinh tong sau = 2 cach s= 1+ (-2) +3 +(-4) + ......+(-98) + 99
Tinh nhanh
1-2-3+3-4-5+.....+97-98-99
B=1/2+1/3+..+1/99+1/100 tren 99/1+98/2+..+2/98+1/99
