Show that if A is measurable set then the set 3A : = { 3a : a Є A} is measurable. Find its measure. How about the set -3A? Give proofs to your answers. [20 marks]
I am not sure how you are defining "measurable", I will assume you mean Jordan measurable.
Also where is a subset of? It will be assumed that .
Let show that and conversely.
Let .
Since is measurable it means can be covered by intervals so that .
If define .
Then cover and .
Thus, is measurable.