mycroft holmes
Last Activity: 10 Years ago
Let A represent the vertex z1, with B and C similarly defined. Let z be the point P
We can write z = t1z1+t2z2+t3z3 = t1z1+t2z2+ (1-t1-t2)z3 so that z-z3 = t1(z1-z3)+ t2(z2-z3).
Since t1,t2>0, this means the vector PC lies in the region between vector AC and BC.
Similarly, you can see that PA lies in the interior of BA and CA, and PB lies in the interior of AB and CB.
The intersection of all these regions in the triangle ABC and its interior thus proving the statement