How many rational terms are contained in the expansion of
a) (2+34)100;
b) (2+33)300?
Show that xy+yz+zx=1 is not solvable in natural numbers.
The board has the form of a cross, which is obtained if corner boxes of a square board of 4×4 are erased. Is it possible to go around it with the help of the knight chess piece and return to the original cell, having visited all the cells exactly once?