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

Toán Lớp 5: tính nhanh: a)1/4 + 1/8 + 1/16 + 1/32 + 1/64 +…+1/512 b)3/4 + 3/8 + 3/16 + 3/32 + 3/64 +…+3/512

Home/ Toán Lớp 5: tính nhanh: a)1/4 + 1/8 + 1/16 + 1/32 + 1/64 +…+1/512 b)3/4 + 3/8 + 3/16 + 3/32 + 3/64 +…+3/512

Toán Lớp 5: tính nhanh: a)1/4 + 1/8 + 1/16 + 1/32 + 1/64 +…+1/512 b)3/4 + 3/8 + 3/16 + 3/32 + 3/64 +…+3/512

Tháng Sáu 13, 2022 Toán học 2 Comments 0 views

Toán Lớp 5: tính nhanh:
a)1/4 + 1/8 + 1/16 + 1/32 + 1/64 +…+1/512
b)3/4 + 3/8 + 3/16 + 3/32 + 3/64 +…+3/512

Comments ( 2 )

  1. thienthanh
    thienthanh
    13 Tháng Sáu, 2022 at 3:00 chiều
    Reply
    Lời giải và giải thích chi tiết:
    a, $\dfrac{1}{4}$ + $\dfrac{1}{8}$ + $\dfrac{1}{16}$ +…+ $\dfrac{1}{512}$
    = $\dfrac{1}{2×2}$ + $\dfrac{1}{2×4}$ + $\dfrac{1}{4×4}$ +…+ $\dfrac{1}{16×32}$
    = $\dfrac{1}{2}$ – $\dfrac{1}{2}$ + $\dfrac{1}{2}$ – $\dfrac{1}{4}$ +…+ $\dfrac{1}{16}$ -$\dfrac{1}{32}$
    = $\dfrac{1}{2}$ – ($\dfrac{1}{2}$ – $\dfrac{1}{2}$) +…+ ($\dfrac{1}{16}$ – $\dfrac{1}{16}$) – $\dfrac{1}{32}$
    = $\dfrac{1}{2}$ – $\dfrac{1}{32}$ 
    = $\dfrac{16}{32}$ – $\dfrac{1}{32}$
    = $\dfrac{15}{32}$
    b, $\dfrac{3}{4}$ + $\dfrac{3}{8}$ + $\dfrac{3}{16}$ +…+ $\dfrac{3}{512}$
    = 3($\dfrac{1}{2×2}$ + $\dfrac{1}{2×4}$ + $\dfrac{1}{4×4}$ +…+ $\dfrac{1}{16×32}$)
    = 3($\dfrac{1}{2}$ – $\dfrac{1}{2}$ + $\dfrac{1}{2}$ – $\dfrac{1}{4}$ +…+ $\dfrac{1}{16}$ -$\dfrac{1}{32}$)
    = 3[$\dfrac{1}{2}$ – ($\dfrac{1}{2}$ – $\dfrac{1}{2}$) +…+ ($\dfrac{1}{16}$ – $\dfrac{1}{16}$) – $\dfrac{1}{32}$]
    = 3[$\dfrac{16}{32}$ – $\dfrac{1}{32}$]
    = 3 × $\dfrac{15}{32}$
    = $\dfrac{45}{32}$

  2. cobebongdem
    cobebongdem
    13 Tháng Sáu, 2022 at 3:00 chiều
    Reply
    a) Gọi A=1/4+1/8+1/16+1/32+1/64+…+1/512
    A=1/4+1/8+1/16+1/32+1/64+…+1/512
    2\timesA=2\times(1/4+1/8+1/16+1/32+1/64+…+1/512)
    2\timesA=1/2+1/4+1/8+1/16+1/32+1/64+….+1/26
    2\timesA-A=1/2+1/4+1/8+1/16+1/32+1/64+….+1/26-(1/4+1/8+1/16+1/32+1/64+…+1/512)
    A=1/2-1/512
    A=255/152
    b) Gọi B=3/4+3/8+3/16+3/32+3/64+…+3/512
    B=3/4+3/8+3/16+3/32+3/64+…+3/512
    2\timesB=2\times(3/4+3/8+3/16+3/32+3/64+…+3/512)
    2\timesB=3+3/2+3/4+3/8+3/16+….+3/128
    2\timesB-B=3+3/2+3/4+3/8+3/16+….+3/128-(3/4+3/8+3/16+3/32+3/64+…+3/512)
    B=3-3/128
    B=381/128
     

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

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