f(x)=2|x+1|+|x-1|>=4√2
解
當(dāng)x=4√2
-2x-2+1-x>=4√2
-3x>=1+4√2
x=4√2-3≈2.656
不滿足假設(shè),舍去
當(dāng)x>=1時(shí)
2(x+1)+(x-1)>=4√2
3x+1>=4√2
x>=(4√2-1)/3≈1.552
∴綜上x(chóng)的取值范圍：x=(4√2-1)/3