有理数绝对值的取法.丨a丨等于------(a>=0) ---------(a<0) 丨a丨等于-------(a<=0)

问题描述:

有理数绝对值的取法.丨a丨等于------(a>=0) ---------(a<0) 丨a丨等于-------(a<=0)

丨a丨等于a(a>=0)
丨a丨等于-a (a≤0﹚