is$($t$)=$ A$1$cos$(1000$t $+$ $/2)+$ A$2$cos$(2000$t $-$ $/2)$

Assume the system is in steady state. Find the current ia at times t$1=4$ ms: ia$($t$1)=$ B$1$ t$2=5$ ms: ia$($t$2)=$ B$2$

Given Variables: A$1$: $1$A A$2$: $1$A L: $1$mH C: $250$ F R$1$: $1$ ohm R$2$: $2$ ohm k: $4$ V$/$A

Calculate the following: B$1($A$)$: