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Geometry Level 2

A B AB is a diameter of a circle with center O . O. Chord C D CD is equal to radius O C . OC. A C AC and B D BD produced intersect at P . P. What is the measure of A P B \angle APB in degrees?

45 60 30 90

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2 solutions

Ayush G Rai
Oct 28, 2016

Join O D . OD. Now O C D \triangle OCD is an equilateral triangle since O C = C D = D O . OC=CD=DO. So, C O D = O D C = D C O = 6 0 . \angle COD=\angle ODC=\angle DCO=60^\circ. Let O D B = O B D = x . [ O D = O B = r a d i u s ] . D O B = 180 2 x . A O C = 2 x 60. \angle ODB=\angle OBD=x.[OD=OB=radius].\angle DOB=180-2x.\angle AOC=2x-60.
Since O A = O C = r a d i u s , O A C = O C A = 120 x . OA=OC=radius,\angle OAC=\angle OCA=120-x. P C D = x . P D C = 120 x . \angle PCD=x.\angle PDC=120-x. Therefore A P B = 180 x 120 + x = 6 0 . \angle APB=180-x-120+x=\boxed{60^\circ}.

this is an easy question i think its from NCERT 9th standard

A Former Brilliant Member - 4 years, 7 months ago

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i dunno.i randomly took it from some book.

Ayush G Rai - 4 years, 7 months ago

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