a+1/a=3
(a+1/a)^2=9
a^2+2+1/a^2=9
a^2+1/a^2=7
a^3+1/a^3
=(a+1/a)(a^2-1+1/a^2)
=3*(7-1)
=3*6
=18
已知a+1/a=3,求a^3+a^(-3)的值,
a+1/a=3
(a+1/a)^2=9
a^2+2+1/a^2=9
a^2+1/a^2=7
a^3+1/a^3
=(a+1/a)(a^2-1+1/a^2)
=3*(7-1)
=3*6
=18