ta co
So hang thu 2 la 3=1+2
So hang thu 3 la 6=1+2+3
So hang thu 4 la 10=1+2+3+4
\(\Rightarrow\)Goi so hang thu 2=>x=1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22
\(\Rightarrow x=\frac{\left(22+1\right)\cdot\left(\frac{\left(22-1\right)}{1}+1\right)}{2}=\frac{23\cdot22}{2}=253\)
Vay so hang thu 22 cua A la 253