Answer
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.
Work Step by Step
The inverse and converse are false statements, so counterexamples can be found.
