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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 6: Bài 9:tính tổng các phân số sau: 2) 2/1.3+2/1.5+2/5.7+…+2/2003.2005 4) 3/4.7+3/7.10+3/10.13+…+3/97.100 Bài 11:Tìm x, biết 1) 2 và 2

Toán Lớp 6: Bài 9:tính tổng các phân số sau:
2) 2/1.3+2/1.5+2/5.7+…+2/2003.2005
4) 3/4.7+3/7.10+3/10.13+…+3/97.100
Bài 11:Tìm x, biết
1) 2 và 2/9 -x =1/12+1/20+1/30+1/42+1/56+1/72
2) (1/2.3+1/3.4+…+1/49.50) . x=1

Comments ( 1 )

  1. text{Bài 9:}
    $\frac{2}{1.3}+\frac{2}{3.5}+…+\frac{2}{2003.2005}$
    $=\frac{1}{1}-\frac{1}{3}+…+\frac{1}{2003}-\frac{1}{2005}$
    $=\frac{1}{1}-\frac{1}{2005}$
    $=\frac{2004}{2005}$
    $\frac{3}{4.7}+\frac{3}{7.10}+…+\frac{3}{97.100}$
    $=\frac{1}{4}-\frac{1}{7}+…+\frac{1}{97}-\frac{1}{100}$
    $=\frac{1}{4}-\frac{1}{100}$
    $=\frac{6}{25}$
    $Bài 11$
    $1)2\frac{2}{9}-x=\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}$
    $\frac{20}{9}-x=\frac{5}{4}$
    $=>x=\frac{20}{9}-\frac{5}{4}$
    $=>x=\frac{145}{72}$
    $2)(\frac{1}{2.3}+…+\frac{1}{49.50}).x=1$
    $=>(\frac{1}{2}-\frac{1}{3}+…+\frac{1}{49}-\frac{1}{50}).x=1$
    $=>(\frac{1}{2}-\frac{1}{50}).x=1$
    $=>\frac{12}{25}x=1$
    $=>x=1:\frac{12}{25}$
    $=>x=\frac{12}{25}$
    text{Chúc bạn học tốt}

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222-9+11+12:2*14+14 = ? ( )