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

Toán Lớp 6: Cho A= 2mủ0+2mủ1+2mủ2+…+2mủ8 và B=4×2mủ7. So sánh A và B Giúp mik vs mn ơi

Toán Lớp 6: Cho A= 2mủ0+2mủ1+2mủ2+…+2mủ8 và B=4×2mủ7. So sánh A và B
Giúp mik vs mn ơi

Comments ( 2 )

  1. A = 2^0 + 2^1 + 2^2 + …….. + 2^8
    ⇔2A = 2 + 2^2 + 2^3 ……… + 2^8
    ⇔2A – A = (2^1 + 2^2 + 2^3 + ……. + 2^9) – (2^0 + 2^1 + 2^2 + ……. + 2^8)
    ⇔ A = 2^9 – 2^1
    B = 4 . 2^7
    B = 2^2 . 2^7
    B = 2^9
    Ta có: 
    2^9 – 2^9
    Mà câu A có 2^9 – 2^1
    ⇒ A < B

  2. A= $2^{0}$ + $2^{1}$ + $2^{2}$ +…+ $2^{8}$
    2A=$2^{1}$ + $x^{2}$ +…+ $2^{8}$ + $2^{9}$
    2A-A=($2^{1}$ + $x^{2}$ +…+ $2^{8}$ + $2^{9}$) – ($2^{0}$ + $2^{1}$ + $2^{2}$ +…+ $2^{8}$)
    A=$2^{9}$ – 1
    B=4 . $2^{7}$= $2^{2}$ . $2^{7}$=$2^{9}$ 
    ⇒$2^{9}$ – 1 < $2^{9}$ 
    Xin hay nhất!

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

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