# Thread: Help with Geometry Concept

1. Good post? |

## Help with Geometry Concept

I do understand you can assume nothing from the diagrams. My question is on the principles.

Here is the question which I've inserted in three photos

My answer would have easily been C - that m and n are equal (the answer is D). I didn't assume that based on the pic. I assumed that because line AD and DC are equal. I thought that equal-sized lines had equal-sized angles. I'm getting this from all the rules on triangles and angles. For instance here:

Can anyone help me get this straight in my head? I feel like a lot of this stuff is just memorization, but I'd like to make valid connections.

2. Good post? |
Hi,
It looks like this is from Princeton review, right?

Actually C is trap answer here.

Actually the opposite angles of equal sides of a triangle are equal.(mind it of a Single triangle)

Here in the first case two sides are equal but that are from different triangle(AD from ADB triangle, DC from BDC triangle); so that formula will not work here.

For the second case, both sides are from a single triangle. So, the formula works here!!!!!!!