Đặt \(A=1+2^2+3^2+...+99^2\)
\(=1.1+2.2+3.3+...+99.99\)
\(=1.1+2.\left(1+1\right)+3\left(2+1\right)+...+99\left(98+1\right)\)
\(=\left(1.2+2.3+3.4+...+98.99\right)+\left(1+2+3+....+99\right)\)
Bạn tự tính tiếp
tinh 1*2+2*3+3*4+...+98*99
tinh 1*99+2*98+3*97+....+98*2+99*1
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
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 sau = 2 cach s= 1+ (-2) +3 +(-4) + ......+(-98) + 99
B=1/2+1/3+..+1/99+1/100 tren 99/1+98/2+..+2/98+1/99
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 nhanh : 2/3*4+2/4*5+2/5*6+...+2/98*99