√（x2+6x+9）+√（x2-2x+1）-√（x2-4x+4）
=√(x+3)²+√(x-1)²-√(x-2)²
=|x+3|+|x-1|-|x-2|
①当x≤-3时,原式=-(x+3)-(x-1)+(x-2)=-x-4
②当-3＜x≤1时,原式=(x+3)-(x-1)+(x-2)=x+2
③当1＜x≤2时,原式=(x+3)+(x-1)+(x-2)=3x
④当x＞2时,原式=(x+3)+(x-1)-(x-2)=x+4