
To form a triangle 3 non collinear points are needed.
Number of ways of selecting 3 points out of 6 can be done in 6C3 = 20 ways.




and sum of radii
are equal.Hence the circle touches externally.
is a vector joining two points P(x1, y1, z1) and Q(x2, y2, z2).If ,Direction cosines of are
Let the sides of the triangle be a=13,b=7 and c=8.
Since a is the longest side the greatest angle is A.
Using Cosine rule, we have