In a circle a diameter #AB# is drawn and on one side of it an arc #CD# is marked, which subtends an angle #50^@# at the center. #AC# and #BD# are joined and produced to meet at #E#. Find #/_CED#?

1 Answer
Feb 2, 2017

#/_CED=65^@#

Explanation:

Consider the following figure, as described in the question, where we have joined #AD# and #BC# and let #/_BOD=x# and #/_AOC=y#.
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As chord #BC# subtends angle #/_BOC# at center and #/_BAE# at the circle, we have #/_BAE=1/2(50+x)=25+x/2#

Similarly for chord #AD#, we have #/_ABE=1/2(50+y)=25+y/2#

Hence #/_CED#, being the third angle of #DeltaABE# is given by

#/_CED=180^@-/_BAE-/_ABE#

= #180^@-25^@-x/2-25^@-y/2=130^@-(x+y)/2#

= #130^@-1/2(180^@-50^@)=130^@-65^@=65^@#