Let the intersection point of the three chords = A
Let the other end of the chord of length 10 = B
Let the other end of the chord of length 12 = C
Connect BC
Let the intersection of BC and chord "x" = D
Let the other end of chord "x" = E
Using the Law of Cosines
BC = sqrt [10^2 + 12^2 - 2 (10*12)cos (60°)] = sqrt ( 244 - 120) = sqrt (124) = 2sqrt (31)
And because angle BAC is bisected then in triangle ABC
BA / CA = BD / CD
10/12 = BD /CD
5/6 = BD / CD
So BD = (5/11)* BC = (5/11)*2sqrt (31) = (10/11) sqrt (31)
And CD = (6/11) * BC = (6/11) * 2sqrt (31) = (12/11)sqrt (31)
And using the Law of Sines
sin ABC / 12 = sin 60 / [ 2sqrt (31)]
sin ABC = 12 sqrt (3) / [ 4sqrt (31) ]
sin ABC = 3sqrt (3) / sqrt (31)
And using the Law of Sines once more
AD / sin ABC = BD / sin BAD
AD / [ 3sqrt (3) /sqrt (31) ] = (10/11)sqrt (31) / sin 30
AD sqrt (31) / [ 3sqrt (3) [ = 2 *(10/11) sqrt (31)
AD = 60 sqrt (3) / 11 = (60/11)sqrt (3)
And using the intersecting chord theorem
AD * DE = BC * CD
(60/11)sqrt (3) * DE = (10/11)sqrt (31) * (12/11)sqrt (31)
(60/11) sqrt (3) * DE = 3720 / 121
(660/121)sqrt (3) * DE = 3720/121
DE = (3720/121) (121/660) / sqrt (3)
DE = (62/11) / sqrt (3)
DE = (62/33)sqrt (3)
So "x" = AD + DE = sqrt(3) ( 60/11 + 62/33) = sqrt (3) ( 180 + 62) / 33 =
sqrt ( 3) (242 / 33 ) = sqrt (3) (22/3) =
22 / sqrt (3)