"Triangle Comparing Ratios of Sides": Why can we assume AC is a straight line?

Link

http://gre.magoosh.com/questions/1072

 

Question

Why can we assume AC is a straight line?

 

Answer

On the GRE, we can't assume that shapes are drawn to scale but we can assume that lines that appear straight are straight - and that's the key point for this question. 

For a more complete list of mathematical conventions on the GRE, we recommend looking over this PDF). Page 4 has an example that is relevant to this question.

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