√27﹣3√1/3=3√3-√3
=2√3
≈3.464第二题会吗？a-1/a=√2(a-1/a)^2=2a^2+(1/a)^2-2=2a^2+(1/a)^2=4a^2+2+(1/a)^2=6(a+1/a)^2=6a+1/a=±√6