a-1/a=2(a-1/a)^2=4a^2+1/a^2-2*a*1/a=4a^2+1/a^2-2=4a^2+1/a^2=6(a^2+1/a^2)^2=36a^4+1/a^4+2=36a^4+1/a^4=34
a-1/a=2 得a=1±√2;(a^2+1/2)^2=?a^2+1/a^2=(a-1/a)^2+2=6;a^4+1/a^4=
a-1/a=2把这个平方，2次方的就好了4次方的同样
