A = 1.2 + 2.3 + 3.4 + ... + 90.91
3A = 1.2.3 + 2.3.3 + 3.4.3 + ... + 90.91.3
3A = 1.2.3 + 2.3.(4 - 1) + 3.4.(5 - 2) + ... + 90.91.(92 - 89)
3A = 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + ... + 90.91.92 - 89.90.91
3A = 90.91.92
A = 90.91.92 : 3 = 251160
tính tổng D= 1.2 + 2.3 + 3.4 + ............. + 90.91
Tính nhanh
C=1.2+2.3+3.4+...+2014.2015
K=1.2+2.3+3.4+..+(n-1).n
Tính
a) S= 1.2+2.3+3.4+...+32.33
b) S= 1.2+2.3+3.4+...+49.50
Tính các biểu thức sau:
C=1.2+2.3+3.4+...+98.99
D=(1.99+2.99+3.99+...99.99)-(1.2+2.3+3.4+...98.99
A= 1.2+2.3+3.4+...........+ 2020.2021
A=1.2+2.3+3.4+...+99.100
Tính:
1.2+2.3+3.4+...+50.51
1.2+2.3+3.4+4.5+...+99.100
cho A = 1/1.2+1/2.3+1/3.4+...+1/49.50 ; cho B = 1.2+1.3+3.4+....+49.50
tính 50mủ 2A - B/17
