√（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當(dāng)x≤-3時(shí),原式=-(x+3)-(x-1)+(x-2)=-x-4
②當(dāng)-3＜x≤1時(shí),原式=(x+3)-(x-1)+(x-2)=x+2
③當(dāng)1＜x≤2時(shí),原式=(x+3)+(x-1)+(x-2)=3x
④當(dāng)x＞2時(shí),原式=(x+3)+(x-1)-(x-2)=x+4