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June 16th, 2015, 07:28 PM  #1 
Senior Member Joined: Jan 2015 From: USA Posts: 107 Thanks: 2  Semicircle and sines and many triangles wow
Hi! Im not sure how to finish this problem. I am attaching what I wrote until my brain crashed can you help me? Is the first part correct? Also I have no idea how to solve the second part. Thanx! 
June 16th, 2015, 08:24 PM  #2 
Math Team Joined: Dec 2013 From: Colombia Posts: 7,502 Thanks: 2511 Math Focus: Mainly analysis and algebra 
If $ABCD$ is a rectangle with the four points in that order on a circle and $AD$ is a diameter, the area of the rectangle is zero because the angle $\angle{ABD}= \angle{ACD} = 90^\circ$.


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semicircle, sines, triangles, wow 
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