Đặt A= 1/4+1/12+1/36+1/108+1/324 +1/972
=1/4.(1+1/3+1/9+1/27+1/81+1/243)
=1/4(1+1/3 +1/3^2 +1/3^3 +1/3^4 +1/3^5)
gọi M=1+1/3+1/3^2+1/3^3+1/3^4+1/3^5
3M=3+1+1/3+1/3^2+1/3^3+1/3^4
3M-M=(3+1+1/3+1/3^2+1/3^3+1/3^4)-(1+1/3+1/3^2+1/3^3+1/3^4+1/3^5)
2M=3-1/3^5
M=3/2-1/3^5.2
A=1/4.(3/2-1/3^5.2)
A=3/8-1/1944=91/243
Vậy .......
Chúc bạn học tốt .....^-^
Tính tổng: 1 + 1/4+ 1/12 + 1/36 + 1/108 +1/324 + 1/972
Tính tổng: 1/4 +1/12 + 1/36 + 1/108 + 1/324 + 1/972
Tính \(\frac{1}{4}+\frac{1}{12}+\frac{1}{36}+\frac{1}{108}+\frac{1}{324}+\frac{1}{972}\)
Tính : A= 1/4 + 1/12 + 1/36+ 1/108+ 1/ 324+ 1/ 972
Các pạn giúp tớ nha . Help me please !
Tính B=\(\frac{1}{4}+\frac{1}{12}+\frac{1}{36}+\frac{1}{108}+\frac{1}{324}+\frac{1}{972}+\frac{1}{2916}+\frac{1}{8748}\)
A=\(\frac{1}{4}+\frac{1}{12}+\frac{1}{36}+\frac{1}{108}+\frac{1}{324}+\frac{1}{972}\)
Tinh:
a) 1/2 + 1/2^2 + 1/3^2 +...+ 1/2^9
b) 1/4 + 1/12 + 1/36 + 1/108 + 1/324 + 1/972
Tính :
a) A=1/2+1/22+1/23+......................................................+1/29
b) B=1/4+1/12+1/36+1/108+1/324+1/972
Tính
\(A=\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^9}\)
\(B=\frac{1}{4}+\frac{1}{12}+\frac{1}{36}+\frac{1}{108}+\frac{1}{324}+\frac{1}{972}\)
