Determine the angle by which v$1$ leads i$1$ if v$1=10$cos$(10$t$-45)$ and i$1$ is equal to $($a$)5$ cos $10$t; $($b$)5$cos$(10$t$-80)$; $($c$)5$cos$(10$t $-40)$; $($d$)5$ cos $(10$t $+40)$; $($e$)5$ sin$(10$t $-19)$