Tính tổng A=2/1.2+2/2.3+2/3.4+…+2/98.99

2 bình luận về “Tính tổng A=2/1.2+2/2.3+2/3.4+…+2/98.99”

1. A = 2/(1xx2) + 2/(2xx3) + 2/(3xx4) +…+ 2/(98xx99)

   A = 2 xx (1/(1xx2)+1/(2xx3)+1/(3xx4)+ … +1/(98xx99))

   A = 2 xx (1/1-1/2+1/2-1/3+ … +1/98-1/99)

   A = 2 xx (1-1/2+1/2-1/3+ … +1/98-1/99)

   A = 2 xx (1-1/99)

   A = 2 xx 98/99 

   A = 196/99 

   @Hel

   Trả lời
2. A = $\frac{2}{1.2}$ + $\frac{2}{2.3}$ + $\frac{2}{3.4}$ + … + $\frac{2}{98.99}$ 

   A = 2 . ( $\frac{1}{1.2}$ + $\frac{1}{2.3}$ + $\frac{1}{3.4}$ + … + $\frac{1}{98.99}$ )

   A = 2 . ( $\frac{1}{1}$ – $\frac{1}{2}$ + $\frac{1}{2}$ – $\frac{1}{3}$ + $\frac{1}{3}$ – $\frac{1}{4}$ + … + $\frac{1}{98}$ – $\frac{1}{99}$ )

   A = 2 . ( $\frac{1}{1}$ – $\frac{1}{99}$ )

   A = 2 .        $\frac{98}{99}$

   A =       $\frac{196}{99}$

   Trả lời