If f (x + 1 / x) = x2 + 1 / x2 + 1, then f (x + 3)=

If f (x + 1 / x) = x2 + 1 / x2 + 1, then f (x + 3)=

Let t = x + 1 / x, then T ^ 2 = x ^ 2 + 1 / x ^ 2 + 2, so x ^ 2 + 1 / x ^ 2 = T ^ 2-2,
So f (T) = T ^ 2-2 + 1 = T ^ 2-1,
Then f (x + 3) = (x + 3) ^ 2-1 = x ^ 2 + 6x + 8