Đáp án:
`f (x) = x^{100} + x^{98} + ... + x^2 - 1`
`text{Vì}` \(\left\{ \begin{array}{l}x^{100}≥0∀x\\x^{98}≥0∀x\\.....\\x^2≥0∀x\end{array} \right.\)
`-> x^{100} + x^{98} + ... + x^2 ≥ 0 ∀x`
`-> x^{100} + x^{98} + ... + x^2 - 1 ≥ -1`
`-> f (x) ≥ -1`
`->` `text{GTNN f (x) = -1}`
`text{Dấu "=" xảy ra khi :}`
`x = 0`
`text{Vậy GTNN f (x) = -1}` `⇔ x = 0`