How do you know when to use the Triangle Midsegment Theorem in a problem?

Hi my sisters and brothers can tell me the answer because i don’t understand the question

In the following diagram it is given that dec,ab || dc, ad || eb, and ad is congruent to bc. a)why isn't abc a parallelogram even though it has a pair of parallel sides and a pair of congruent sides b)explain why be must be congruent to bc. further explain what type of triangle this makes triangle abc and what it tells you about angle 1 and angle 2c) finally why must angle 3 be congruent to angle 1? further, explain why we know that angle 3 is congruent to angle 2

Which is f(5) for the function –2x2 + 2x - 3?