Question

Rewrite the definition “Perpendicular lines form right angles” as a biconditional statement using “if and only if”

Answer 1

Well, to write the definition of "Perpendicular lines form right angel" using "if and only if". the sentence would become :

Two lines are perpendicular if and only if they form a right angle

Hope this helps

Answer 2

 "Two perpendicular lines form right angles." 
p = two lines are perpendicular 
q = two lines form right angles 

p --> q ≡ IF two lines are perpendicular THEN two lines form right angles. 

converse will be: q --> p 
q -->p ≡ IF two lines form right angles THEN two lines are perpendicular. 
this is always true. and there is no counterexample to it. 
therefore q --> p is also always true because this is the definition of two perpendicular lines is fact. 

so we can write bi-conditional statement as p <--> q and say two lines are perpendicular IF AND ONLY IF two lines form right angles.