Prove that if the two angles on the base of a trapezoid are different, then the diagonal starting from the smaller angle is longer than the other diagonal.
KURSCHAK 1955
Kürschák Competition 1955.
Other problems
How many five digit numbers are divisible by and contain the digit ?
The vertices of a triangle are lattice points (they have integer coordinates). There are no other lattice points on the boundary of the triangle, but there is exactly one lattice point inside the triangle. Show that it must be the centroid.