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

Toán Lớp 6: Tính A = 4 + 12 + 24 + -+ 19800

Home/ Toán Lớp 6: Tính A = 4 + 12 + 24 + -+ 19800

Toán Lớp 6: Tính A = 4 + 12 + 24 + -+ 19800

Tháng Bảy 18, 2022 Toán học 1 Comment 0 views

Toán Lớp 6: Tính A = 4 + 12 + 24 + ….+ 19800

Comments ( 1 )

  1. daithanh
    daithanh
    18 Tháng Bảy, 2022 at 3:54 chiều
    Reply
    A = 4 + 12 + 24 + …. + 19404 + 19800
    => 1/2 A = 1/2 . ( 4 + 12 + 24 + ….+ 19800 )
    => 1/2 A = 2 + 6 + 12 + … + 9702 + 9900
    => 1/2 A = 1 . 2 + 2 . 3 + 3 . 4 + … + 98 . 99 + 99 . 100
    => 1/2 . A . 3 = 3 . ( 1 . 2 + 2 . 3 + 3 . 4 + … + 98 . 99 + 99 . 100 )
    => 3/2 A = 1 . 2 . 3 + 2 . 3 . 3 + 3 . 4 . 3 + …. + 98 . 99 . 3 + 99 . 100 . 3
    => 3/2 A = 1 . 2 . 3 + 2 . 3 . ( 4 – 1 ) + 3 . 4 .( 5 – 2 ) + … + 98 . 99 . ( 100 – 97 ) + 99 . 100 . ( 101 – 98 )
    => 3/2 A =  1 . 2 . 3 + 2 . 3 . 4 – 1 . 2 . 3 + 3 . 4 . 5 – 2 . 3 .4 + … + 99 . 100 . 101 – 98 . 99 . 100
    => 3/2 A = 99 . 100 . 101
    => 3/2 A = 999900
    => A = 999900 : 3/2
    => A = 666600
     

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

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