B is BD⊥AC, AC is D.
∵BD⊥AC
∴ Deriving RT△ABD
∠∠ADB+∠A+∠ABD = 180,∠A=60,∠ADB=90
∴∠ABD=30
∫RT△ABD
∴ ad =1* ab (the right angle side of RT triangle facing 30 degrees is half of the hypotenuse)
∫AB = 15
∴AD=7.5
Derived from Pythagorean theorem
BD=( 15 root number 3)/2
∫AC = AD = DC,AD=7.5
∴DC=33/2
∵BD⊥AC
∴RT△BDC
Derived from Pythagorean theorem
BC^2=DC^2+BD^2
BC=2 1cm
Hope to adopt