\(=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}\)
\(\frac{1}{2}-\frac{1}{8}=\frac{4}{8}-\frac{1}{8}=\frac{3}{8}\)
Tính nhanh: A=1/6+1/12+1/20+1/30+1/42+1/56
Tính nhanh:
A = 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56
Tính
1. A= 1/2+1/6+1/12+/1/20+1/30+1/42+1/56
2. B = 3/2+5/6+7/12+-9/20+11/30-13/42+15/56
Tính nhanh
8/9-1/72-1/56-1/42-1/30-1/20-1/12-1/6-1/2
bài 2: tính nhanh :
a) 3/8 + 7/12 + 10/16 + 10/24 b) 4/6 + 7/13 + 17/9 + 19/13 + 1/9 + 14/6
c) 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56
Tính nhanh :
A = 1/2 + 1/3 + 1/6 + 1/12 + 1/15 + 1/20 + 1/30 + 1/35 + 1/42 + 1/56 + 1/63 + 1/72 + 1/99
Tính nhanh:
A=\(\frac{1}{90}-\frac{1}{72}-\frac{1}{56}-\frac{1}{42}-\frac{1}{30}-\frac{1}{20}-\frac{1}{12}-\frac{1}{6}-\frac{1}{2}\)
B=\(\frac{3}{2}-\frac{5}{6}+\frac{7}{12}-\frac{9}{20}+\frac{11}{30}-\frac{13}{42}+\frac{15}{56}-\frac{17}{72}\)
Tính nhanh
a, 1/2 + 5/6 + 11/ 12 + 19/20 + 29/30 + 41/42 + 55/56 + 71/72 + 89/90
b, (1+1/2).(1+1/3)+......+(1+1/2011)
a) tính tổng A= 1/6+1/12+1/20+1/30+1/42+1/56
cho mình cả cách làm ạ^^