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Toán Lớp 6: a. A=3 + 3^2 + 3^3+-+3^39 + 3^40 b. B=2^50 – 2^49 -2^48 – 2^47= 2^2 – 2

Home/ Toán Lớp 6: a. A=3 + 3^2 + 3^3+-+3^39 + 3^40 b. B=2^50 – 2^49 -2^48 – 2^47= 2^2 – 2

Toán Lớp 6: a. A=3 + 3^2 + 3^3+-+3^39 + 3^40 b. B=2^50 – 2^49 -2^48 – 2^47= 2^2 – 2

Hằng Anh Tháng Tám 29, 2022 Toán học 1 Comment 0 views

Toán Lớp 6: a. A=3 + 3^2 + 3^3+….+3^39 + 3^40
b. B=2^50 – 2^49 -2^48 – 2^47……..- 2^2 – 2

Comments ( 1 )

annhocbichchaubich
29 Tháng Tám, 2022 at 6:54 sáng

Reply

a)A=3+3^2+3^3+…+3^39+3^40

=>3.A=3^3+3^3+3^4+…+3^41

=>3A-A=(3^3+3^3+3^4+…+3^41)-(3+3^2+3^3+…+3^39+3^40)

=>2A=3^41-3

=>A=(3^41-3)/2

b)B=2^50-2^49-2^48-2^47-…-2^2-2

Đặt A=2^49+2^48+2^47+…+2

=>2A=2^50+2^49+2^48+…+2^2

=>2A-A=(2^50+2^49+2^48+…+2^2)-(2^49+2^48+2^47+…+2)

=>A=2^50-2

=>B=2^50-A

=>B=2^50-2^50+2

=>B=2

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