Question

If $\angle 1+\angle 2=180,$then $l$and $m$are ___________.

Answer 1

If then $l$and $m$are $parallel$ ($\angle 1$and $\angle 2$are $interioranglesonsamesideoftransversal$)

for Sum of $interioranglesonsamesideoftransversal$to be ${180}^o$or ($\angle 1+\angle 2=180,$) lines $l$and $m$must be $parallel$