A=(x-1)(x+2)(x+3)(x+6)+12
=(x-1)(x+6)(x+2)(x+3)+12
=(x2+6x-x-6)(x2+3x+2x+6)+12
=(x2+5x)2-6.6+12
=(x2+5x)2-36+12
=(x2+5x)2-24
\(\Rightarrow\) (x2+5x)2\(\ge\)0 voi moi x
\(\Rightarrow\) (x2+5x)2\(\ge\) -24
Vay GTNN la -24
Dấu "=" xảy ra khi : x2+5x=0
x(x+5)=0
=>x=0 va -5
Nhớ k nha