Geometry

jayhawk2001: Community Manager; Posts: 789; Joined: Sun Jan 28, 2007 3:51 pm; Location: Silicon valley, California; Thanked: 30 times; Followed by:1 members

by jayhawk2001 » Wed May 30, 2007 5:41 pm

Triangle ABC is equilateral since AB = BC = AC = radius.
So, angle CAB = 60.

Similarly, angle CAD = 60.

In triangle ABD, we have AB = AD. So, corresponding angles = x

120 + 2x = 180, x = 30 degrees

Is it B?

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gviren: Senior | Next Rank: 100 Posts; Posts: 44; Joined: Fri Mar 30, 2007 3:11 pm

by gviren » Wed May 30, 2007 8:18 pm

spot on.... OA is 30

Thanks for your response

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drhomler: Master | Next Rank: 500 Posts; Posts: 141; Joined: Thu May 03, 2007 1:15 pm

by drhomler » Thu Jun 07, 2007 5:39 am

Jay in this particular problem I came up with 30 degrees too but for clarity sake, can you really assume that the two interior angles are equal without knowing that BD was parallel to the diameter? Because if it wasnt than the interior angles of x and triangle ABD might not be equal?

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jayhawk2001: Community Manager; Posts: 789; Joined: Sun Jan 28, 2007 3:51 pm; Location: Silicon valley, California; Thanked: 30 times; Followed by:1 members

by jayhawk2001 » Thu Jun 07, 2007 7:07 am

drhomler wrote:Jay in this particular problem I came up with 30 degrees too but for clarity sake, can you really assume that the two interior angles are equal without knowing that BD was parallel to the diameter? Because if it wasnt than the interior angles of x and triangle ABD might not be equal?

Yes, In triangle ABD, since AB = AD, corresponding angles have to be
equal to x

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