Unit Step Function: u(-t) Meaning & Negative Time

[amaresh92]

what does the u(-t) mean in unit step funtion in basic function of signal and system?how can be time taken as -ve?

 

[n.karthick]

u(t) is unit step function right? It means that u=1 for t>=0 and u=0 otherwise.
In the same way u(-t) can be understood. That is u=1 for t<=0 and u=0 otherwise.
Here time is not taken as -ve but only the argument to u is taken as -ve.