Tính S=1/2+1/3+...+1/72 .giúp mk nha
Tính nhanh: A= 1/3 - 3/4 -( -3/5) + 1/72 - 2/9 - 1/36 + 1/15
Giải chi tiết giúp mk nha
Tính: 1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90-1/3-1/15-1/35-1/63-1/99-1/143
Các bạn giúp mk nhanh nha
1-1/2+1/2-1/3+1/3+1/4-1/4+1/5-1/5+1/6-1/6+1/7-1/7+1/8-1/8+1/9-1/9+1/10-(1-1/3+1/3-3/5+3/5-4/7+5/9-5/9+6/11-6/11-7/13)=1+1/10-1+7/13=83/130
Câu hỏi : Tính Nhanh
B = 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90 + 1/100 + 1/132
Làm ơn ! Hãy giúp mk nhanh nha ! Ai làm đc thì mk tick cho bn đó đúng 3 tick ! Mk nói là làm nha !
\(B=\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+...+\frac{1}{132}\)
\(B=\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+...+\frac{1}{11\cdot12}\)
\(B=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{11}-\frac{1}{12}\)
\(B=\frac{1}{4}-\frac{1}{12}\)
\(B=\frac{1}{6}\)
Tính nhanh :
B = 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90 + 1/110 + 1/132
B = 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8 + 1/8.9 + 1/9.10 + 1/10.11 + 1/11.12
B = 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + 1/7 - 1/8 + ...... + 1/11 - 1/12
B = 1/4 - 1/12
B = 3/12 - 1/12
B = 2/12
B = 1/6
giúp mk nha
cho Sn= 1 - 2 + 3 - 4 + ... + (-1)n-1 x n với n = 1, 2, 3 ,..
tính S35 + S60
Các bn thấy dễ hông
Làm hộ mk nha
Bài ôn tập cuối năm của lớp mk
Tính B=8/9-1/72-1/56-1/42-1/30-1/20-1/12-1/6
Giúp mk nha mn
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Tính tổng S = 1 + \(\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^{100}}\)
Các bn giúp mk nha !!!
\(S=1+\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{100}\)
\(\Rightarrow2S=2+1+\frac{1}{2}+\frac{1}{2^2}...+\frac{1}{99}\)
\(2S-S=\left(2+1+\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{99}}\right)-\left(1+\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{100}}\right)\)
\(\Leftrightarrow2S-S=S=2-\frac{1}{2^{100}}=\frac{2^{101}}{2^{100}}-\frac{1}{2^{100}}=\frac{2^{101}-1}{2^{100}}\)
1)Tìm x, biết:
a) 3*x+54:2=230
b)( 30+1/2+0.5*3-1.5):(9/2-7/2)*(1.45*x)=10
2) Tìm x,y biết:
số 1996xy chia hết cho 2,5,9
3) Tính:
1/56+1/72+1/90+.....+1/9900
giúp mk nha
1.
a) 3x + 54 : 2 = 230
3x + 27 = 230
3x = 230 - 27
3x = 203
x = 203: 3
x = \(\frac{203}{3}\)
Vậy x = \(\frac{203}{3}\)
1 ) \(3.x+54:2=230\)
\(3.x+27=230\)
\(3.x=230-27\)
\(3x=203\)
\(x=203:3\)
\(x=\frac{203}{3}\)
b) \(\left(30+\frac{1}{2}+0,5.3-1,5\right):\left(\frac{9}{2}-\frac{7}{2}\right).\left(1,45.x\right)=10\)
\(\left(\frac{61}{2}+1,5-1,5\right):1.\left(1,45.x\right)=10\)
\(30,5:1.\left(1,45.x\right)=10\)
\(30,5.\left(1,45.x\right)=10\)
\(1,45.x=10:30,5\)
\(1,45.x=\frac{20}{61}\)
\(x=\frac{20}{61}:1,45\)
\(x=\frac{400}{1769}\)
Tính tổng S=\(\frac{1+2+2^2+2^3+...+2^{2008}}{1-2^{2009}}\)
Làm giúp mk bài này nha!Cảm ơn mn nhiều:3
1/56+1/72+1/90+....+1/9900
giúp mk nha
\(\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+...+\frac{1}{9900}\)
\(=\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}+....+\frac{1}{99.100}\)
\(=\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+......+\frac{1}{99}-\frac{1}{100}\)
\(=\frac{1}{7}-\frac{1}{100}\)
\(=\frac{93}{100}\)
\(\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+...+\frac{1}{9900}\)
\(=\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}+...+\frac{1}{99.100}\)
\(=\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}+...+\frac{1}{99}-\frac{1}{100}\)
\(=\frac{1}{7}-\frac{1}{100}=\frac{93}{700}\)
\(\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+...+\frac{1}{9900}\)
\(=\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}+....+\frac{1}{99.100}\)
\(=\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+......+\frac{1}{99}-\frac{1}{100}\)
\(=\frac{1}{7}-\frac{1}{100}\)
\(=\frac{93}{100}\)