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

Toán Lớp 5: Tính các tổng sau : A = 1/6 + 1/12 + 1/20 + 1/30 + … + 1/9900

Toán Lớp 5: Tính các tổng sau :
A = 1/6 + 1/12 + 1/20 + 1/30 + … + 1/9900

Comments ( 2 )

  1. A = 1/6 + 1/12 + 1/20 + 1/30 + …. + 1/19900
    A = 1/( 2 xx 3 ) + 1/( 3 xx 4 ) + 1/( 4 xx 5 ) + 1/( 5 xx 6 ) + …. + 1/( 99 xx 100 )
    A = 1/2 – 1/3 + 1/3 – 1/4 + 1/4 – 1/5 + 1/5 – 1/6 + …. + 1/99 – 1/100
    A = 1/2 – 1/100
    A = 49/100
    ** Công thức : a/( n xx ( a + n ) ) = a/n – a/( a + n )

  2. A = 1/6 + 1/12 + 1/20 + 1/30 + … + 1/9900
    A = 1/(2×3) + 1/(3×4) + 1/(4×5) + 1/(5×6) + … + 1/(99×100)
    A = 1/2 – 1/3 + 1/3 – 1/4 + 1/4 – 1/5 + 1/5 – 1/6 + … + 1/99 – 1/100
    A = 1/2 – 1/100
    A = 50/100 – 1/100
    A = 49/100
     

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

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