He didn’t know______ or stay until the end of the festival.

A. whether to go

B. if that he should go

C. to go

D. if to go

Đặt: \(A=x^2+3x+4=x^2+2.x.\dfrac{3}{2}+\dfrac{9}{4}+\dfrac{7}{4}\)

\(A=\left(x+\dfrac{3}{2}\right)^2+\dfrac{7}{4}\)

Ta có: \(\left(x+\dfrac{3}{2}\right)\ge0\)

\(\Rightarrow A=\left(x+\dfrac{3}{2}\right)^2+\dfrac{7}{4}\ge\dfrac{7}{4}\)

\(\Rightarrow Min_A=\dfrac{7}{4}\) khi \(x=\dfrac{-3}{2}\)