sina=BC/AB
cosa=AC/AB
sin^2x+cos^2x=1
cos^2x=1-sin^2x
cos^2x=64/289
cosx=8/17
8/17=8/AB
AB=8*17/8=17
По теореме Пифагора:
AB^2=AC^2+CB^2
-CB^2=AC^2-AB^2
CB^2=AB^2-AC^2
CB^2=289-64=225
CB=15
ответ: 15.
cosA=ac/ab; 1=cos2α + sin2α. 1=cos2α+225/289
cos2α= 64/289
cosα = 8/17
8/17= 8/ab
ab= 17
AB2=BC2+AC2
BC2 =AB2-AC2
BC2=289-64=225
BC=15.
Удачи =)
