SD
S D
если cosA=sqrt5/3, то sinA=sqrt(1-5/9)=2/3, AB=BC/sinA=15
AB = c
AC = a
BC = b = 10
a/c = root(5)/3
c = 3*a/root(5)
a = root(c^2 - b^2)
c = 3*root(c^2 - b^2)/root(5)
c^2 = 9 * (c^2 - 100)/5
5*c^2 = 9*c^2 - 900
900 = 9*c^2 - 5*c^2
c^2 = 900/4
c = root(9*25)
c = 3*5 = 15
AB = 15