Solution:
Let P be a good point. Let l,m,n be respectively the number of parts the sides BC,CA,AB are divided by the rays starting from P. Note that a ray must pass through each of the vertices of the triangle ABC; otherwise we get some quadrilaterals.
Let h1 be the distance of P from BC. Then h1 is the height for all the triangles with their bases on BC. Equality of areas implies that all these bases have equal length. If we denote this by x, we get lx=a. Similarly, taking y and z as the lengths of the bases of triangles on CA and AB respectively, we get my=b and nz=c. Let h2 and h3 be the distances of P from CA and AB respectively. Then
h1x=h2y=h3z=272Δ
where Δ denotes the area of the triangle ABC. These lead to
h1=272Δal,h2=272Δbm,h3=272Δcn
But
a2Δ=ha,b2Δ=hb,c2Δ=hc
Thus we get
hah1=27l,hbh2=27m,hch3=27n
However, we also have
hah1=Δ[PBC],hbh2=Δ[PCA],hch3=Δ[PAB]
Adding these three relations,
hah1+hbh2+hch3=1
Thus
27l+27m+27n=hah1+hbh2+hch3=1
We conclude that l+m+n=27. Thus every good point P determines a partition (l,m,n) of 27 such that there are l,m,n equal segments respectively on BC,CA,AB.
Conversely, take any partition (l,m,n) of 27. Divide BC,CA,AB respectively into l,m,n equal parts. Define
h1=27a2lΔ,h2=27b2mΔ
Draw a line parallel to BC at a distance h1 from BC; draw another line parallel to CA at a distance h2 from CA. Both lines are drawn such that they intersect at a point P inside the triangle ABC. Then
[PBC]=21ah1=27lΔ,[PCA]=27mΔ
Hence
[PAB]=27nΔ
This shows that the distance of P from AB is
h3=27c2nΔ
Therefore each triangle with base on CA has area 27Δ. We conclude that all the triangles which partition ABC have equal areas. Hence P is a good point.
Thus the number of good points is equal to the number of positive integral solutions of the equation l+m+n=27. This is equal to
(226)=325