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簡而言之就是一句話:“任何實數的絕對值都是非負數!”
(1)若x≥0時,丨x丨-x=x-x=0; (2)若x<0時,丨x丨-x=-x-x=-2x>0; 由(1)(2)可得丨x丨-x表示的數是非負數. 故選D.
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