f(x)=|x-4|+|x+2|,若f(x)=k無解，則k為？

f(x)=(x-4)^2+(x+2)^2=k 可視為(4,0),(-2,0)之橢圓 無解表不在線上
所以 k<((4-(-2))^2)^(1/2) ==> k<6

k<6

In Elliptic Paraboloid z=x^2/a^2 + y^2/b^2 ;Treating (4,0), (-2,0) as x and y terms;
Then z=4^2+4=20.as an analysis.