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

Toán Lớp 6: 1) x – ( 18 – x ) = x – 9 2) Cho T = 5 + $5^{2}$ + $5^{3}$ + … + $5^{2020}$

Toán Lớp 6: 1) x – ( 18 – x ) = x – 9
2) Cho T = 5 + $5^{2}$ + $5^{3}$ + … + $5^{2020}$

Comments ( 2 )

  1. Giải đáp + Lời giải và giải thích chi tiết:
    Bài 1 : 
    x – ( 18 – x ) = x – 9
    => (18 – x ) = 9
    => x = 18 – 9
    => x = 9
    Bài 2 : 
    T = 5 + 5^2 + 5^3 + …….. + 5^2020
    5T = 5^2 + 5^3 + 5^4 + ……. + 5^2021
    5T – T = (5^2 + 5^3 + 5^4 + ……. + 5^2021) – (5 + 5^2 + 5^3 + …….. + 5^2020)
    4T = 5^2021 – 5
    => T = (5^2021 – 5)/4

  2. 1)x-(18-x)=x-9
    =>x-(18-x)-x=x-9-x
    =>-(18-x)=-9
    =>18-x=9
    =>x=18-9
    =>x=9
    Vậy x=9
    2)T=5+5²+5³+…+5^2020
    =>5T=5( 5+5²+5³+…+5^2020)
    =>5T=5²+5³+5⁴+…+5^2021
    =>5T-T=(5²+5³+5⁴+…+5^2021)-(5+5²+5³+…+5^2020)
    =>4T=5^2021 -5
    =>T=(5^2021 -5)/4
    Vậy T=(5^2021 -5)/4

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