Question

What should be used as perpendicular of triangle dbe ? that teacher ssays df is perpendicular , but how??????? , length of that df is different

Answer 1

DF and EG both can be perpendicular...

some perpendicular lie outside the triangle

Answer 2

no df is not perpendicular of triangle dbe...
EG is the perpendicular for DBE as DB is the base and when it is extended EG is the perpendicular....

so EG is the perpendicular
hope it helps