a) Ta có : G(x) = -( 3x+2 )^2 + 2( 3x+7 ) - 17
<=> G(x)= - ( 3x+2 )^2 + 2( 3x+7 ) -1 - 16
<=> G(x)= - [ ( 3x+2 )^2 - 2( 3x+7 ) +1 ] - 16
,<=> G(x)= - [ ( 3x+2 )-1 ]^2 - 16
Vì - [ ( 3x+2 )-1 ]^2 <= 0 vs mọi x
nên - [ ( 3x+2 )- 1]^2 - 16 <= -16 vs mọi x
b) Ta có : - [ ( 3x+2 )-1 ]^2 -16 <= -16...