ai nhanh tick nha m.n

Question

tính

Answer 1

Đặt A = 

Ta có : -2.A = -2( )

-2.A = 2/3 + 2/15 + 2/35 + ...+ 2/9999

-2.A= 2/1.3+2/3.5+2/5.7+...+2/99.101

-2.A = 1-1/3+1/3-1/5+1/5-1/7+...+1/99-1/101

-2.A= 1-(1/3-1/3)-(1/5-1/5)-...-(1/99-1/99)-1/101

-2.A= 1-0-0-0-...-0-1/101

-2.A= 1-1/101

-2.A = 101/101 - 1/101

-2.A=100/101

A= 100/101 : (-2)

A=100/101 . -1/2

A=-50/101

Vậy A= -50/101