Question

[Đoàn Thu Thuỷ]

Tìm x

\(\frac{x-2}{4}=\frac{5+x}{2}\)

Rút gọn biểu thức

\(A=1+\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^{2012}}\)

Answer 1

[Oh Nova]

a/ (x-2)/4 =5+x/2

=> \(\frac{x-2}{4}\) = \(\frac{x+5}{2}\)

=> 2(x-2) = 4(x+5)

2x-4 =4x+20

4x-2x=-20-4

2x=-24

x=-12

Answer 2

[Oh Nova]

sr chua hết

b/ A = 1 +1/2 +1/2² +.....+1/2²⁰¹²

=> 2A=2 +1 /2 +1/2 +....+1/2²⁰¹¹

=> 2A-A=2 +1 /2 +1/2 +....+1/2²⁰¹¹ - (1 +1/2 +1/2² +.....+1/2²⁰¹²⁾)

=> A=2-1/2²⁰¹²