表达式3: "f" left parenthesis, "x" , right parenthesis equals negative "x" times "k" times left parenthesis, 1 negative abs left parenthesis, StartFraction, "x" Over "r" , EndFraction , right parenthesis , right parenthesis left brace, abs left parenthesis, "x" , right parenthesis less than "r" , right brace 有图表。 要进行音频跟踪,按“Alt 键 + T”。fx=−x·k·1−absxrabsx<r