Question

tìm GTNN,GTLN:

a) A=x³-3x+5

b) B=(2x-1)²+(x+2)²

c) C=4-x²+2x

d) D=4x-x²

Answer 1

a\(A=x^2-3x+5\)

\(\Leftrightarrow A=x^2-2.\dfrac{3}{2}x+\dfrac{9}{4}+5-\dfrac{9}{4}\)

\(\Leftrightarrow A=\left(x-\dfrac{3}{2}\right)^2+\dfrac{11}{4}\ge\dfrac{11}{4}\)

Min \(A=\dfrac{11}{4}\Leftrightarrow x=\dfrac{3}{2}\)

Answer 2

c) \(C=4-x^2+2x\)

\(\Leftrightarrow C=-\left(x^2-2x+4\right)+8\)

\(\Leftrightarrow C=-\left(x-2\right)^2+8\le8\)

Max \(C=8\Leftrightarrow x=2\)

Mấy câu kia tương tự ,bạn làm nhé