Question

gia tri nho nhat cua bieu thuc A=x^2+2x+5

Answer 1

A= x^2+2x +5

   =x^2+2x+1+4

   =(x+1)² +4

=>A_min=4

Answer 2

\(A=x^2+2x+5=\left(x^2+2x+1\right)+4=\left(x^2+2.x.1+1^2\right)+4\)

\(=\left(x+1\right)^2+4\)

Vì \(\left(x+1\right)^2\ge0=>\left(x+1\right)^2+4\ge4\) (với mọi x)

Dấu "=" xảy ra \(< =>\left(x+1\right)^2=0< =>x=-1\)

Vậy minA=4 khi x=-1