Final answer:
The three biconditional statements that are true are: 1) The number 117 is divisible by 9 if and only if the sum of the digits in 117 is evenly divisible by 9. 2) 10 + 10 = 20 if and only if 2 × 10 = 20. 3) A rhombus is a square if and only if its opposite angles are equal.
Step-by-step explanation:
The three biconditional statements that are true are:
a) "The number 117 is divisible by 9 if and only if the sum of the digits in 117 is evenly divisible by 9."
c) "10 + 10 = 20 if and only if 2 × 10 = 20."
d) "A rhombus is a square if and only if its opposite angles are equal."
These statements hold true because they express a two-way logical relationship. In each statement, both conditions must be true for the biconditional statement to be true.