# Commuting Operators

#### Raptor112

1. The problem statement, all variables and given/known data
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?

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#### TSny

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?
$M_2 + M_1M_2$

#### TSny

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?
$(1 +M_1)M_2$ ?

#### TSny

Homework Helper
Gold Member
Yes.

"Commuting Operators"

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