1
Part of 1989 IMO Longlists
Problems(2)
Multiplication table for the new product for n=11 and n=12
Source: IMO Longlist 1989, Problem 1
9/18/2008
In the set S_n \equal{} \{1, 2,\ldots ,n\} a new multiplication is defined with the following properties:
(i) c \equal{} a * b is in for any
(ii) If the ordinary product is less than or equal to then a*b \equal{} a \cdot b.
(iii) The ordinary rules of multiplication hold for i.e.:
(1) a * b \equal{} b * a (commutativity)
(2) (a * b) * c \equal{} a * (b * c) (associativity)
(3) If a * b \equal{} a * c then b \equal{} c (cancellation law).
Find a suitable multiplication table for the new product for n \equal{} 11 and n \equal{} 12.
algebra unsolvedalgebra
Equal to the area of the quadrangle
Source: IMO Longlist 1989, Problem 100
9/18/2008
If in a convex quadrilateral and are the midpoints of the sides and respectively. Show that the sum of the areas of the triangles and is equal to the area of the quadrangle.
geometrygeometry unsolved