已知a²-3a-1=0,求a²+1/a²,a³-1/a³,a³+1/a³的值

a²-3a-1=0∴ a≠0∴ a-3-1/a=0∴ a-1/a=3(1) 平方a²+1/a²-2=9∴ a²+1/a²=11(2) a³-1/a³=(a-1/a)(a²+1+1/a²)=3*(11+1)=36(3)(a+1/a)²= a²+1/a²+2=13∴ ...为什么a²+1/a²-2=9∴ a²+1/a²=11？移项啊，a²+1/a²-2=9a²+1/a²=9+2=11