For the 48 th question, both the first and OR question are related to each other.
1. You have to add the first statement [a b c] = 0. then proceed as told. To prove this we write box product of all the vectors to be proven coplanar i.e. [(a+b) (b+c) (c+a)]. open this completely and write 0 whenever [a b c] or box product with 2 same vectors appear. final answer is 0. therefore (a+b), (b+c), (c+a) is coplanar.
2. start by [(a+b) (b+c) (c+a)]. open it but only substitute 0 for box product with 2 same vectors. your final result would be 2[a b c].