Expression 4: "f" Subscript, 2 , Baseline left parenthesis, "x" , right parenthesis equals "t" plus StartFraction, 1 Over left parenthesis, StartNestedFraction, 1 NestedOver left parenthesis, "x" minus "t" , right parenthesis , EndNestedFraction minus StartNestedFraction, 1 NestedOver 1 minus "t" , EndNestedFraction plus StartNestedFraction, 1 NestedOver "l" minus "t" , EndNestedFraction , right parenthesis , EndFraction left brace, "x" greater than or equal to "t" , right brace Has graph. To audio trace, press ALT+T.f2x=t+11x−t−11−t+1l−tx≥t