\(=\frac{32+16+8+4+2+1}{64}=\frac{63}{64}\)

ai nhanh mình k

1 /2 -1 /4 + 1 /8-1 /16 + 1 /32-1 /64 < 1 /3

Cách 1:21/64 < 1/3

Cách 2:21/64 < 0.(3)

Đúng

1 /2 + 1 /4 + 1 /8 + 1 /16 + 1 /32 + 1 /64 < 1 /3

Cách 2:63/64 < 0.(3)

Ko đúng

Câu 3 mình ko biết

a)cho \(\frac{1}{2}-\frac{1}{4}+\frac{1}{8}-\frac{1}{16}+\frac{1}{32}-\frac{1}{64}\)là A

ta có:A=\(\frac{1}{2}-\frac{1}{4}+\frac{1}{8}-\frac{1}{16}+\frac{1}{32}-\frac{1}{64}\)

2A=\(\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{8}-\frac{1}{16}+\frac{1}{32}-\frac{1}{64}\right)2\)

2A=\(1-\frac{1}{2}+\frac{1}{4}-\frac{1}{8}+\frac{1}{16}-\frac{1}{32}\)

2A+A=\(\left(1-\frac{1}{2}+\frac{1}{4}-\frac{1}{8}+\frac{1}{16}-\frac{1}{32}\right)+\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{8}-\frac{1}{16}+\frac{1}{32}-\frac{1}{64}\right)\)

3A=\(1-\frac{1}{64}\Rightarrow3A=\frac{63}{64}\Rightarrow A=\frac{21}{64}< \frac{1}{3}\)

vậy \(\frac{1}{2}-\frac{1}{4}+\frac{1}{8}-\frac{1}{16}+\frac{1}{32}-\frac{1}{64}< \frac{1}{3}\)

b) sai đề (\(\frac{63}{64}< \frac{1}{3}\)hay sao)

c)sai nối (nếu x=y=3 thì 2x+3y=17 chia hết nhưng 9x+5y=42 ko chia hết)

bằng -55/72

Có phải bạn soạn nhầm 16 thành 6 đúng không :) 

\(\frac{\frac{15}{8}-\frac{15}{16}-\frac{15}{32}+\frac{15}{64}}{3-\frac{3}{2}-\frac{3}{4}+\frac{3}{8}}\)

\(=\frac{15.\left(\frac{1}{2}-\frac{1}{4}-\frac{1}{8}+\frac{1}{16}\right)}{6.\left(\frac{1}{2}-\frac{1}{4}-\frac{1}{8}+\frac{1}{16}\right)}\)

\(=\frac{15}{6}\)

\(=\frac{5}{2}\)

6 chứ ko phải 16 đâu bạn

\(\dfrac{2x}{15}+\dfrac{2x}{35}+\dfrac{2x}{63}+...+\dfrac{2x}{195}=\dfrac{4}{5}\\ x\cdot\left(\dfrac{2}{15}+\dfrac{2}{35}+\dfrac{2}{63}+...+\dfrac{2}{195}\right)=\dfrac{4}{5}\\ x\cdot\left(\dfrac{2}{3\cdot5}+\dfrac{2}{5\cdot7}+\dfrac{2}{7\cdot9}+...+\dfrac{2}{13\cdot15}\right)=\dfrac{4}{5}\\ x\cdot\left(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{13}-\dfrac{1}{15}\right)=\dfrac{4}{5}\\ x\cdot\left(\dfrac{1}{3}-\dfrac{1}{15}\right)=\dfrac{4}{5}\\ x\cdot\dfrac{4}{15}=\dfrac{4}{5}\\ x=\dfrac{4}{5}:\dfrac{4}{15}\\ x=3\)

Gọi \(D=\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{8}-\dfrac{1}{16}+\dfrac{1}{32}-\dfrac{1}{64}\)

\(2D=1-\dfrac{1}{2}+\dfrac{1}{4}-\dfrac{1}{8}+\dfrac{1}{16}-\dfrac{1}{32}\\ 2D+D=\left(1-\dfrac{1}{2}+\dfrac{1}{4}-\dfrac{1}{8}+\dfrac{1}{16}-\dfrac{1}{32}\right)+\left(\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{8}-\dfrac{1}{16}+\dfrac{1}{32}-\dfrac{1}{64}\right)\\ 3D=1-\dfrac{1}{2}+\dfrac{1}{4}-\dfrac{1}{8}+\dfrac{1}{16}-\dfrac{1}{32}+\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{8}-\dfrac{1}{16}+\dfrac{1}{32}-\dfrac{1}{64}\\ 3D=1-\dfrac{1}{64}< 1\\ \Rightarrow D=\dfrac{1-\dfrac{1}{64}}{3}< \dfrac{1}{3}\)

Vậy \(\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{8}-\dfrac{1}{16}+\dfrac{1}{32}-\dfrac{1}{64}< \dfrac{1}{3}\)

x - ( 81 + 5x ) = 19

=> x - 81 - 5x = 19

=> ( x - 5x ) - 81 = 19

=> -4x = 19 + 81

=> -4x = 100

=> x = 100 : ( -4 )

=> x = -25

2x - ( 8 + 3x ) = 92

=> 2x - 8 - 3x = 92

=> ( 2x - 3x ) = 8 + 92

=> -x = 100

=> x = -100

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