Đặt S= 52+53+54+...+5100
5S=53+54+...+5100+5101
=> 5S-S=(53+54+...+5100+5101) - (52+53+54+...+5100)
4S= 5101-52
S= \(\frac{5^{1001}-5^2}{4}\)
nhan 5 voi tong tren roi tru di tong ban dau chia cho 4 la ra(khi tru cho tong ban dau co cac hang tu lap nhau)
Đặt A=52+53+54+…+5100
5A=53+54+…+5100+5101
4A=5101-52
A= (5101-52):4
đặt A=52+53+54+...+5100
5A=53+54+55+...+5101
5A-A=5101-52
4A=5101-52
A=(5101-52):4
