√[(x-4)²(6-x)]
=|x-4|√(6-x)
当x-4≥0,6-x≥0,即4≤x≤6时
√[(x-4)²(6-x)]=(x-4)√(6-x)
所以√[(x-4)²(6-x)]=(x-4)√(6-x)成立的条件是4≤x≤6