It is proved that equation 1 + X + x ^ 2 + x ^ 3 / 6 = 0 has and only has one real root, which is proved by Rolle's theorem

It is proved that equation 1 + X + x ^ 2 + x ^ 3 / 6 = 0 has and only has one real root, which is proved by Rolle's theorem

First, we prove the existence of the zero point theorem
Let f (x) = 1 + X + x ^ 2 / 2 + x ^ 3 / 6
And f (0) = 1 > 0
F (- 2) = - 1 / 30, so contradictory, so the root is unique!
The original equation has and has only one real root