A=1/1+2+1/1+2+3+1/1+2+3+4+...+1/1+2+3+...+150 GIÚP MÌNH VỚI !

A = $\frac{1}{1+2}$ + $\frac{1}{1+2+3}$ + ... + $\frac{1}{1+2+..+150}$ 

A = $\frac{1}{3}$ + $\frac{1}{6}$ + ... + $\frac{1}{150.151:2}$ 

$\frac{1}{2}$ A = $\frac{1}{6}$ + $\frac{1}{12}$ + ... + $\frac{1}{150.151}$ 

$\frac{1}{2}$ A = $\frac{1}{2.3}$ + $\frac{1}{3.4}$ + ... + $\frac{1}{150.151}$ 

$\frac{1}{2}$ A = $\frac{1}{2}$ - $\frac{1}{3}$ + $\frac{1}{3}$ - $\frac{1}{4}$ + ... + $\frac{1}{150}$ - $\frac{1}{151}$ 

$\frac{1}{2}$ A = $\frac{1}{2}$ - $\frac{1}{151}$ = $\frac{151}{302}$ - $\frac{2}{302}$ = $\frac{149}{302}$ 

A = $\frac{149}{302}$ . 2 = $\frac{149}{151}$ .

Vậy A = $\frac{149}{151}$.