1. The problem statement, all variables and given/known data Prove the points of the open interval (a,b) are those of the form a + t(b-a) for 0 < t < 1. 2. Relevant equations 3. The attempt at a solution I'm interpreting this as asking me to prove that if x is in (a,b), then x can be written as a + t(b-a) for some 0 < t < 1. Conversely, it's asking me to prove that if x = a + t(b-a) with 0 < t < 1, then x is in (a,b). Is this interpretation correct?