sinA
=
sinB
=
sinC
=kとおくと,sinA=5k, sinB=6k, sinC=7k
5
6
7
正弦定理より,
a
=
b
=
c
=2Rだから,a=2RsinA=10kR, b=2RsinB=12kR, c=2RsinC=14kR
sinA
sinB
sinC
よって,a:b:c=10kR:12kR:14kR=10:12:14=
5:6:7