Two questions on Perm com
1. Let there be m and n points on two straight lines in a plane(not necessarilly parallel). Join all the points in every way possible. Prove that other than the m+n points lying on the two lines, the number of intersectionss is mn(m-1)(n-1)/2 2.
Let there be 2n lines on a plane of lengths 1,2,3,.....2n. Prove that the number of possible triangles from these lines is n(n-1)(4n-5)/6