Đáp án:
`A=63/64`
Giải thích các bước giải:
`A= 1/2+1/4+1/8+1/16+1/32+1/64`
`<=>1/2+1/2^2+1/2^3+1/2^4+1/2^5+1/2^6`
`<=>1/2 A=1/2^2+1/2^3+1/2^4+1/2^5+1/2^6+1/2^7`
`<=>A-1/2A=1/2-1/2^7`
`<=>1/2A=1/2-1/2^7`
`<=>` $A=\dfrac{\dfrac{1}{2}-\dfrac{1}{2^7}}{\dfrac{1}{2}}$
`<=>` $A=\dfrac{\dfrac{1}{2}.(1-\dfrac{1}{2^6})}{\dfrac{1}{2}}$
`<=>A=1-1/2^6`
`<=>A=63/64`
