b)-3(x2-3x+9/4)+27/4
=-3(x-3/2)2+27/4=<27/4
Dấu "=" xảy ra khi x-3/2=0<=>x=3/2
Vậy MaxB=27/4 <=>x=3/2
a)\(A=2x^2-8x-10=2\left(x^2-4x-5\right)=2\left(x^2-4x+4\right)-18\)
\(=2\left(x-2\right)^2+18\ge18.\)
b)\(B=9x-3x^2=-3\left(x^2-\frac{3}{2}\right)^2+\frac{27}{4}\le\frac{27}{4}\)
Vậy GTLN của B là 27/4
b)-3(x2-3x+9/4)+27/4
=-3(x-3/2)2+27/4=<27/4
Dấu "=" xảy ra khi x-3/2=0<=>x=3/2
Vậy MaxB=27/4 <=>x=3/2
b)-3(x2-3x+9/4)+27/4
=-3(x-3/2)2+27/4=<27/4
Dấu "=" xảy ra khi x-3/2=0<=>x=3/2
Vậy MaxB=27/4 <=>x=3/2
b)-3(x2-3x+9/4)+27/4
=-3(x-3/2)2+27/4=<27/4
Dấu "=" xảy ra khi x-3/2=0<=>x=3/2
Vậy MaxB=27/4 <=>x=3/2