Question

The AB//CD,CD//EF,AB//EF prove.

Answer 1

AB||CD
as ABC = BCD by alternate interior angles
CD || EF
as sum of interior angle is 160+20 = 180
AB ||EF
as AB || CD and CD|| EF
Then AB|| EF because line parallel to same line r parallel to each other
Hope it helps

Answer 2

$< abc = < bcd = 40 since \: these \: are \: corresponding \: angle \: hence \: ab \: parallel \: cd \\ 2) \: < ECD + < cef \: = 180 hence \: ef \: parallel \: cd \\ 3)ab \: parallel \: cd \: parallel \: ef$