Show [J2, J+] = 0 - Homework Solution

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SUMMARY

The discussion focuses on proving that the commutator [J2, J+] equals zero, where J+ is defined as Jx + i Jy. The solution involves breaking down the left-hand side (L.H.S.) into components, specifically [J2, Jx] and [J2, Jy], both of which are established to be zero. The final conclusion confirms that L.H.S. equals the right-hand side (R.H.S.), validating the initial statement. The confusion regarding the extraction of 'i' from the bracket in Step 3 is addressed, emphasizing that it is permissible due to the linearity of the commutator.

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Homework Statement



To show [J2, J+] = 0

2. Homework Equations


J+ = Jx + i Jy

[J2, Jx ] = 0

[J2, Jy ] = 0

The Attempt at a Solution



Step 1: L.H.S. = [J2, J+]

Step 2: L.H.S. = [J2, Jx + i Jy ]

Step 3: L.H.S. = [J2, Jx ] + i [J2, Jy ]

Step 4: L.H.S. = 0 + 0

Step 5: L.H.S. = 0

L.H.S. = R.H.S.

I'm kinda confuse about 'Step 3'. Can we take out the 'i' from whole bracket? If yes, then do I have to give any reason for it?
 
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Go ahead and write out the full commutator in step 2. What do you get?
 

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