# Are these Linear and Time Invariant Systems?

We were given the above systems and we were asked to tell whether they are linear (or not) and time invariant(or not).

1. $y(m,n)=x(m,n)+c,\quad c>0$

2. $y(m,n)=x(m,n)+x(m,-n)$

3. $y(m,n)=x(m,n+m)$

4. $y(m,n)=x(m,n) + y(m-a,n-b)$

Although I know the theory for the signal to be linear and time invariant I have trouble applying it. Can any of you explain one of the above so I can continue on my own for the rest of them? Thank you in advance

• Hi, welcome to DSP SE. What did you do so far? Where are you stuck? Did you do some searching on the website? There is already many answers to such questions. – jojek Apr 13 '16 at 23:22
• Thanks for editing my question, actually i have problem proving all these without having the analytic form of the signal x. – johny Apr 13 '16 at 23:38