Register Now

Login

Lost Password

Lost your password? Please enter your email address. You will receive a link and will create a new password via email.

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

Toán Lớp 5: tính nhanh :1.A=1/2 x3 + 1/ 3 x 4 + 1/ 4 x5 +…+1/ 19x 20 2.B=5/ 2 x3 + 5/3 x4 + 5/ 4 x5 +…+ 5/ 19 x20

Tháng Sáu 13, 2022 Toán học 2 Comments 0 views

Toán Lớp 5: tính nhanh :1.A=1/2 x3 + 1/ 3 x 4 + 1/ 4 x5 +…+1/ 19x 20
2.B=5/ 2 x3 + 5/3 x4 + 5/ 4 x5 +…+ 5/ 19 x20

Comments ( 2 )

  1. thanhthuythu
    thanhthuythu
    13 Tháng Sáu, 2022 at 12:03 chiều
    Reply
    A = 1/(2 xx 3) + 1/(3 xx 4) + 1/(4 xx 5) + … + 1/(19 xx 20)
    A = 1/2 – 1/3 + 1/3 – 1/4 + 1/4 – 1/5 + … + 1/19 – 1/20
    A = 1/2 – 1/20
    A = 9/20
    ___________________________________
    B = 5/(2 xx 3) + 5/(3 xx 4) + 5/(4 xx 5) + … + 5/(19 xx 20)
    B = 5 . (1/(2 xx 3) + 1/(3 xx 4) + 1/(4 xx 5) + … + 1/(19 xx 20) )
    B = 5 . (1/2 – 1/3 + 1/3 – 1/4 + 1/4 – 1/5 + … + 1/19 – 1/20)
    B = 5 . (1/2 – 1/20)
    B = 5 . 9/20
    B = 9/4

  2. thudan
    thudan
    13 Tháng Sáu, 2022 at 12:02 chiều
    Reply
    A = 1/{2 × 3} + 1/{3 × 4} + 1/{4 × 5} + … + 1/{19 × 20}
    A = 1/2 – 1/3 + 1/3 – 1/4 + 1/4 – 1/5 + … + 1/19 – 1/20
    A = 1/2 – 1/20
    A = 9/20
    Vậy A = 9/20
    —
    B = 5/{2 × 3} + 5/{3 ×4} + 5/{4 × 5} + … + 5/{19 × 20}
    B = 5×(1/{2 × 3} + 1/{3 × 4} + 1/{4 × 5} + … + 1/{19 × 20})
    B = 5×(1/2 – 1/3 + 1/3 – 1/4 + 1/4 – 1/5 + … + 1/19 – 1/20)
    B = 5 × (1/2 – 1/20)
    B = 5 × 9/20
    B = 45/20
    #dtkc

Leave a reply

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

Phi Nhung

About Phi Nhung