## Geometry: Common Core (15th Edition)

Converse: If $a+d=b+c$, then a, b, c and d form a 2-by-2 calendar square. Inverse: If a, b, c and d do not form a 2-by-2 calendar square, then $a+d\ne b+c$. The same counterexamples can be used to show that the converse and inverse are false. Four consecutive squares lettered a-d is a counterexample. (i.e. a=1, b=2, c=3, d=4) Such numbers satisfy the equality but are not a calendar square. Four consecutive even numbered squares lettered a-d is a counterexample. (i.e. a=2, b=4, c=6, d=8) Such numbers satisfy the equality but are not a calendar square.