$2.$ Classify each of the following systems $=()$ as $($a$)$ linear or nonlinear $($b$)$ time$-$invariant or

time$-$varying $($c$)$ dynamic or static $($d$)$ causal or non causal. Assume every input $$ is a causal

signal. Also $()$ denotes unit step function.

a$.()+3()=22()+(+2).$

b$.()=$ sin$((+10)).$

c$.()=$ sin$2()()$

$$

$$ $.$