ta xet
1/1.2-1/2.3=1/1.2.3
1/2.3-1/3.4=1/2.3.4
...................
1/37.38-1/38.39=1/37.38.39
=>2b=(2/1.2.3+2/2.3.4+.................+2/37.38.39)
=(1/1.2-1/2.3+..............+1/37.38-1/38.39)
=(1/1.2-1/38.39)
=370/741
=>B=185/741
k nh
1/1.2.3+1/2.3.4+1/3.4.5+...+1/37.38.39
1/1.2.3+1/2.3.4+1/3.4.5+....+1/37.38.39 = ?
1/1.2.3+1/2.3.4+1/3.4.5+...+1/37.38.39
1/1.2.3+1/2.3.4+1/3.4.5+...+1/37.38.39
Tính tổng A= 1/1.2.3 +1/2.3.4+1/3.4.5+.......+1/37.38.39
1/1.2.3+1/2.3.4+1/3.4.5+......+1/37.38.39 =?
tinh A= 1/1.2.3 + 1/2.3.4 +1/3.4.5 + ... +1/36.37.38 +1/ 37.38.39
Tính nhanh\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{37.38.39}\)
Tính:
\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{37.38.39}\)