Triangle ABC has side AB=AC, and angle BAC = 20 degrees.
D is a point on side AC with AD=BC. Find angle DBC.
Solve this without trigonometry.
(In reply to
first part by Jim)
Since we know angle EDA is 80, EDC has to be 100.
Now draw a line EB, which will interset AC at point F.
The angles about point F are 60 and 120.
AFB is 120, and CAB is 20, so FBA is 40. (just so happens FBC is also 40).
now, FB has to equal Fd (but now I forgot why) so FDB = FBD. (iso triangle).
If FBD = 30 and FBA = 40, then DBA = 10, CBA (80) - DBA (10) = 70.
OK, someone tell me again why FB = FD.
And why is it when I submit posts, my screen goes gray?????
I have to clear cache and restart computer to get perplexus back!!
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Posted by Jim
on 2004-09-09 14:31:31 |
re: first part
