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2A=1+1/2+1/4+1/8+1/16+1/32+1/64
2A-A=(1+1/2+1/4+1/8+1/16+1/32+1/64)-(1/2+1/4+1/8+1/16+1/32+1/64+1/128)
A=1-1/128
A=127/128
A = 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128
suy ra: 2A = 1 + 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64
2A - A = 1 + 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 - 1/2 - 1/4 - 1/8 - 1/16 - 1/32 - 1/64 - 1/128
A = 1 - 1/128 = 127/128
hok tốt
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28 : x + 12 : x = 5
( 28 + 12 ) : x = 5
40 : x = 5
x = 40 : 5 = 8
Chúc bạn học tốt
\(\frac{28}{x}+\frac{12}{x}=5\)
\(\frac{28+12}{x}=\frac{5}{1}\)
\(=\frac{40}{x}=\frac{5}{1}\)
Ta lấy: \(\frac{40}{x}=\frac{40\div8}{x\div8}=\frac{5}{1}\)
Vậy: \(x=8\)
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2y=\(1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}+\frac{1}{128}\)
2y-y=1-\(\frac{1}{256}\)
y=\(\frac{255}{256}\)
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128 x y - 12 x y - 16 x y = 5208000
(128 - 12 - 16) x y = 5208000
100 x y = 5208000
y = 5208000 : 100
y = 520800