Chứng minh: 1x3x5x7x…………x39
A= ____________________=1/2^20
21x22x23x……..x40
Chứng minh: 1x3x5x7x…………x39 A= ____________________=1/2^20 21x22x23x..
By Eliza
By Eliza
Chứng minh: 1x3x5x7x…………x39
A= ____________________=1/2^20
21x22x23x……..x40
$A = \dfrac{1.3.5.7…39}{21.22.23….40}$
$ = \dfrac{(21.23…..39)(1.3…19)}{21.22.23….40}$
$ = \dfrac{1.3…19}{22.24….40}$
$ = \dfrac{1.3….19}{2.11.2.12.2.13….2.20}$
$ = \dfrac{1.3…19}{2^{20}.(11.12…..20)}$
$ = \dfrac{1}{2^{20}} $