"a" would be the answer if we assumed that a ,b and c > 0
However......to cover all situations......assume that a < 0 and bc < 0
Then the answer is l a l
To see why :
√ [abc] * √ [ a / (bc) ] = √ [ (a^2 * bc ) / ( bc)] = √ a^2
If "a" < 0 and we wrote down "a" as a result......we would be obtaining a negative value from a positive root.......which isn't possible