tTDXY

摘要： \[a_{n+1}=\sqrt{\smash[b]{S_{n}^2+S_n+1}},a_1=1,\text{求}a_n \]\[a_{n+1}^2=S_n^2+S_n+1 \]\[cos{\frac{2\pi}{3}}=\frac{S_n^2+1^2-a_{n+1}^2}{2\times S_n\t 阅读全文