Question

Is this correct? proving similarity

Answer 1

question attached. my answer:

There is not enough information to prove similarity, because we only know that two sides are proportional.

Answer 2

You have two pairs of parallel sides so their corresponding angles will be equal to each other.

Answer 3

@quickstudent
You see what I mean?

Answer 4

http://prntscr.com/c9ehlk

Answer 5

Do the little lines on the sides mean they are parallel?

Answer 6

Yes.

Answer 7

So first you start your proof by saying that they are parallel.

Answer 8

What do you do next?

Answer 9

@quickstudent @~

Answer 10

I'm not sure, I don't get it

Answer 11

@Conqueror @Evoker @kewlgeek555 @mathmate @zepdrix

Answer 12

yes

Answer 13

I'm not writing a two column proof, I just have to use a postulate to prove the two are similar. But the only way I see that possible is with SAS postulate, but how would I know if the two sides are proportional?

Answer 14

@agent0smith @Conqueror @Evoker @mathmate @zepdrix

Answer 15

@quickstudent

This is one of the ambiguities of the question.
In geometry, what is not told cannot be assumed.

Most people would assume that the points A,D,C,E are collinear because they appear to be. If that was given, we can use corresponding angles on the parallel lines.

On the other hand, the author has a moral duty to indicate clearly what appears to be is not the case. If the points are meant not to be collinear, they should have drawn AC clearly not parallel to DE.

This question was probably designed by a non-mathematical person who does not know the conventions. Questions like this will get students to start assuming things that are not given to be true and get away with it.

Answer 16

Yeah, there's LOTS of questions like that in my class.... that's what makes it really difficult for me sometimes :(

So how do you think I should answer this question?

Answer 17

there seems to be plenty of information if you ask me since it shows you the proportions and which ones are parallel to one another

Answer 18

Proportions? I see the parallel, but how do you know they are proportional?

Answer 19

@quickstudent

I sympathize with your situation.

In your place, I would say no, we cannot prove that the triangles are similar, because of lack of information (we're not given that B,D,C,E are collinear, so cannot assume).

However, it depends on your school's culture. Perhaps your teacher expects you to assume things that are not given explicitly, then you end up losing points for this one.

Weigh the pros and cons and decide based on that.

Perhaps someone else will provide better help!

:(