(1-1/4).(1-1/9)......(1-1/100)
=1/1-1/4.1/4-1/9....1/9-1/100
=1/1-1/100
=99/100
\(\left(1-\frac{1}{4}\right).\left(1-\frac{1}{9}\right).....\left(1-\frac{1}{100}\right)\)
= 3/4.8/9.....99/100
= 3.8....99/4.9....100
=1.3.2.4.....9.11/2.2.3.3....10.10
= (1.2.3....9) . (3.4...11)/(2.3.4....10).(2.3.4...10 )
=11/10.2 = 11/20
k mk nha bn