Question

Tìm gtln của bt: -x^2-4x+9

Answer 1

Ta có : -x²-4x+9

=-x²-4x-4+13

=-(x²+4x+4)+13

=-(x+2)²+13

=13-(x+2)²

\(\Rightarrow\)(x+2)²\(\ge\)0

Ma: 13>0 \(\Leftrightarrow\)(x+2)²\(\le\)13

Vay GTLN la 13

Dau "=" xay ra khi : x+2=0

                                 x=-2

Answer 2

-x^2-4x+9=-(x^2+4x+4-13)=-(x+2)^2+13 

ta co -(x+2)^2 nho hon hoac bang 0

               13 lon hon 0

nen bt tren se nho hon hoac bang 13

 dau = xay ra <=> x+2=0=>x=-2

vay min bt =13 tai x=-2