Đặt A = 1.2+2.3+3.4+........+99.100
=> 3A = 1.2.(3 - 0) + 2.3.(4 - 1) + ..... + 99.100.(101 - 98)
=> 3A = 1.2.3 - 1.2.3 + 2.3.4 - 2.3.4 + ..... + 99.100.101
=> 3A = 99.100.101
=> A = 99.100.101/3
=> A = 333300
so sanh (a+1).(a+2).(a+3)-a.(a+1).(a+2) va 3(a+1).(a+2)
b,tinh
M=1.2+2.3+3.4+...+ 2002.2003
GIUP MINH NHANH LEN NHE CAC BAN!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
1.2 + 2.3 + 3.4+...+ ( n - 1 ) .n
giup mk cau nay nhe
s=1.2+2.3+3.4+....+99.100 giup minh voi
tnh bang cach hop li neu co the
1/2*3 +1/3.4 + 1/4*5 + ..... + 1/39*40
giup minh voi nhe mai phai nop rui
a, tinh tong D=1.2+2.3+3.4+...+99.100
b, su dung ket qua cau a tinh nhanh:
E=12+22+32+...+982+992
c, tinh nhanh: F=1.100+2.99+3.98+...+98.3+99.2+100.1
minh can lam giup minh voiiii....
tinh tong
D=1.2+2.3+3.4+.....+99.100
Trả lời dùm nha C:
M = 1/1.2 + 1/2.3 + 1/3.4 + 1/3.4 + ... + 1/2019.2020
