# Commuting Operators

Raptor112

## Homework Statement

It is known that ##M_1,M_2, M_3## commute with each other but I don't see how the second line is achieved even though it says that it's using that ##M_1## and ##M_2## commute?

## Answers and Replies

Homework Helper
Gold Member
Note M2(1+M1) = M2 + M2M1

How can you rewrite the right hand side using the fact that M1 and M2 commute?

Raptor112
Note M2(1+M1) = M2 + M2M1

How can you rewrite the right hand side using the fact that M1 and M2 commute?

##M_2 + M_1M_2##

Homework Helper
Gold Member
##M_2 + M_1M_2##
OK. Can you see something you can do with this expression that will help?

Raptor112
OK. Can you see something you can do with this expression that will help?
##(1 +M_1)M_2## ?

Homework Helper
Gold Member
Yes.