See complete Problem 180 at:

www.gogeometry.com/problem/p180_circle_triangle_quadrilateral_area.htm

Circles Tangent Externally, Common External Tangents, Areas. Level: High School, SAT Prep, College geometry

Post your solutions or ideas in the comments.

## Monday, September 22, 2008

### Elearn Geometry Problem 180

Labels:
area,
circle,
common tangent,
external,
quadrilateral,
tangent,
triangle

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1.

ReplyDeletefor 2 fixed touching circle, CD is unique, so is EF

reflect CD to C'D' by AB, C'D' touch the circle, C'=E and D'=F, and obvious that S_1=S_2

2.

mACD+mCDB=180°, AC//BD, [BCD]=[BAD], S=S_1+S_2 is obvious