已知關于x的函數(shù)y=f(x),y=g(x)與h(x)=kx+b(k,b∈R)在區(qū)間D上恒有f(x)≥h(x)≥g(x).
(1)若f(x)=x
2+2x,g(x)=-x
2+2x,D=(-∞,+∞),求h(x)的表達式;
(2)若f(x)=x
2-x+1,g(x)=klnx,h(x)=kx-k,D=(0,+∞),求k的取值范圍;
(3)若f(x)=x
4-2x
2,g(x)=4x
2-8,h(x)=4(t
3-t)x-3t
4+2t
2(0<|t|≤
),D=[m,n]?[-
,
],求證:n-m≤
.