2－x≥0,得：x≤2
则：x－3≤0、x－4≤0

√(x²－6x＋9)＋√(x²－8x＋16)
=√(x－3)²＋√(x－4)²
=|x－3|＋|x－4|
=(3－x)＋(4－x)
=7－2x