Q=1/4(1.4/2.3+2.5/3.4+3.6/4.5+...+48.51/49.50)
=1/4(2.3−2/2.3+3.4−2/3.4+4.5−2/4.5+...+49.50−2/49.50)
=1/4(1− 2/2.3+ 1− 2/3.4+ 1− 2/4.5+...+1− 2/49.50)
=1/4[48−2(1/2.3+1/3.4+...+1/49.50)]
=1/4[48−2(1/2−1/3+1/3−1/4+...+1/49−150)]
=14[48−2(1/2−1/50)]=294/25
tính 2.4+3.5+4.6+5.7+6.8+7.9+8.10+...+97.99+98.100
Tính
a,B=2.4+4.6+6.8+...+98.100
b,B=3+3.6+6.9+...+96.99
Tính
a, 2.4+4.6+6.8+......+100.102
b, 8.10+10.12+12.14+.....+98.100
c, 1.2.3+2.3.4+4.5.6+5.6.7
Bài tập: Tính tổng
a) A = 1.2+2.3+3.4+...+98.99
b) B = 1.3+3.5+5.7+...+99.101
c) S = 1.4+4.7+7.10+...+2017.2020
d) E= 2.4+4.6+6.8+...+98.100
e) S= 1.2.3+2.3.4+3.4.5+...+98.99.100
f) S= 1.2.3.4+2.3.4.5+3.4.5.6+...+19.20.21.22
tính nhanh
\(1.3+2.4+3.5+4.6+...+48.50+49.51\)
\(1.4+2.5+3.6+...+98.101+99.102\)
2.4+4.6+6.8+...+98.100/1.2+2.3+3.4+...+49.50. Tính
Tính nhanh:(1/2.4)+(1/4.6)+(1/6.8)+.....+(1/98.100)=
Tính 4/4.6+4/6.8+4/8.10+....+4/28.30
Tính tổng
5/4.6+5/6.8+5/8.10+....+5/298.300
