$a)f\left(x\right)=3x-6x^2+2\left(x^2-1,5x\right)=3x-6x^2+2x^2-3x=-4x^2$   

$a=-4,b=0,c=0$  

$b)f\left(x\right)=x^2-2\left(\sqrt{2}{x}^2+4\right)=x^2-2\sqrt{2}{x}^2-8=\left(1-2\sqrt{2}\right)x^2-8$