Tĩnh T=1/2+1/6+1/12+1/20+...+1/9900
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T= 1 - 1/2 + 1/2 - 1/3 + ......+ 1/99 - 1/100
= 1 - 1/100
= 99/100
\(t=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{99.100}\)
\(t=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{99}-\frac{1}{100}\)
\(t=1-\frac{1}{100}=\frac{99}{100}\)
Vậy \(t=\frac{99}{100}\)
T= 1/1.2+1/2.3+1/3.4+...+1/99.100
T=1-1/2+1/2-1/3+1/3-1/4+...+1/99-1/100
T=1- 1/100
T= 99/100
đúng cho mình nha bạn
Bài này đơn giản mà bạn
Biến đôi T = \(\frac{1}{1.2}+\frac{1}{2.3}+.....+\frac{1}{99.100}\)
\(T=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-......-\frac{1}{100}\)
\(T=\frac{100}{100}-\frac{1}{100}=\frac{99}{100}\)
ta có : t = 1/1.2 + 1/2.3 + 1/3.4 + .... + 1/98.99 + 1/99.100
=> t = 1/1 - 1/2 + 1/2 - 1/3 + .... + 1/99 - 1/100
=> t = 1 - 1/100
=> t = 99/100
T=1/1x2+1/2x3+1/3x4+....................+1/98x99+1/99x100
T=1-1/2+1/2-1/3+..............+1/98-1/99+1/99-1/100
T=1-1/100
T=99/100
T=1/2+1/6+1/12+..............+1/9702+1/9900
T=1/1x2+1/2x3+1/3x4+...........+1/98x99+1/99x100
T=1-1/2+1/2-1/3+1/3-1/4+.........+1/98-1/99+1/99-1/100
T=1-1/100
T=99/100
Vậy T=99/100
Giải :
Đặt : A = \(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+....+\frac{1}{9702}+\frac{1}{9900}\)
\(\Rightarrow A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+....+\frac{1}{98.99}+\frac{1}{99.100}\)
\(\Rightarrow A=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\)
\(\Rightarrow A=1-\frac{1}{100}=\frac{99}{100}\)
T = \(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+...+\frac{1}{98\cdot99}+\frac{1}{99\cdot100}=\)
T = \(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}=\)
T = \(\frac{1}{1}-\frac{1}{100}=\)
T = \(\frac{99}{100}\)
= 1/1.2 + 1/2.3 + 1/3.4 + 1/4.5 +....+1 /99.100
= 1/1 - 1/2 + 1/2 -1/3 + .... + 1/99 - 1/100
= 1/1 - 1/100
= 100/100 - 1/100
= 99/100
1/2+1/6+1/12+1/20+...+1/9900
=1/1.2+1/2.3+1/3.4+...+1/99.100
=1-1/2+1/2-1/3+1/3-1/4+...+1/99-1/100
=1-1/100=99/100
Cach giai nhu vay ne ban: T= 1/2 + 1/6+ 1/12+ 1/20+ ......+ 1/9900 T= 1/1*2 + 1/2*3+ 1/3*4+......+ 1/99*100 T= 1/1-1/2+1/2-1/3+1/3-1/4+......+1/99-1/100 T= 1-1/100= 99/100 DS: 99/100 [ PS: dau * la dau nhan nhe ban! ]
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