A = \(x^2\) + 5\(x\) + 100
A = \(\left(x^2+5x+\frac{25}{4}\right)\) + \(\frac{375}{4}\)
A = (\(x\) + \(\frac54\))\(^2\) + \(\frac{375}{4}\)
(\(x+\frac54\))\(^2\) ≥ 0
(\(x+\frac54\))\(^2\) + \(\frac{375}{4}\) ≥\(\frac{375}{4}\)
Amin = \(\frac{375}{4}\) khi \(x=-\frac54\)