Question

Tìm GTLN

C=(2-x)(x+4)

Answer 1

\(=2x+8-x^2-4x\)

\(=-x^2-2x+8\)

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

\(=-\left(x^2+2x+1-9\right)\)

\(=-\left(x+1\right)^2+9< =9\)

Dấu '=' xảy ra khi x=-1

Answer 2

C = (2 - x) (x + 4)

= x(2 - x) + 4 (2 - x)

Answer 3

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

    \(=2x+8-x^2-4x\)

    \(=-x^2-2x+8\)

    \(=9-\left(x+1\right)^2\le9\)

Dấu = xảy ra khi x+1=0  \(\Leftrightarrow x=-1\)

Vậy \(Max_C=9\) tại x=-1