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Contests
National and Regional Contests
India Contests
India Pre-Regional Mathematical Olympiad
2018 India PRMO
8
8
Part of
2018 India PRMO
Problems
(1)
2018 preRMO p8, angle chasing with a chord
Source:
8/8/2019
Let
A
B
AB
A
B
be a chord of a circle with centre
O
O
O
. Let
C
C
C
be a point on the circle such that
∠
A
B
C
=
3
0
o
\angle ABC =30^o
∠
A
BC
=
3
0
o
and
O
O
O
lies inside the triangle
A
B
C
ABC
A
BC
. Let
D
D
D
be a point on
A
B
AB
A
B
such that
∠
D
C
O
=
∠
O
C
B
=
2
0
o
\angle DCO = \angle OCB = 20^o
∠
D
CO
=
∠
OCB
=
2
0
o
. Find the measure of
∠
C
D
O
\angle CDO
∠
C
D
O
in degrees.
angles
geometry
chord