Operators A & B Commute: Explain Why or Why Not?

In summary, the conversation is about determining whether two operators, A and B, commute. The specific example being discussed is when A is the square root operator and B is the square operator. The textbook says that these two operators do not commute, and the conversation goes on to discuss why this is the case. Ultimately, it is determined that the two operations do not commute because not all functions can be squared rooted, thus making the statement ##(\sqrt{f(x)})^2 = \sqrt{(f(x))^2}## not always true.
  • #1
terp.asessed
127
3

Homework Statement


Determine whether or not the following pairs of operators commute...and there was one I could not solve...according to the back of the textbook, I do understand 14.c does NOT commute, but I don't understand...

(14)c.
A = SQR
B = SQRT

Homework Equations


ABf(x) - BAf(x) = 0

The Attempt at a Solution


ABf(x) = A[f(x)]1/2 = f(x)
BAf(x) = Bf2(x) = f(x)...so I thought they DO commute, but the textbook says NO! Could someone explain? Thanks!
 
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  • #2
terp.asessed said:

Homework Statement


Determine whether or not the following pairs of operators commute...and there was one I could not solve...according to the back of the textbook, I do understand 14.c does NOT commute, but I don't understand...

(14)c.
A = SQR
B = SQRT

Homework Equations


ABf(x) - BAf(x) = 0

The Attempt at a Solution


ABf(x) = A[f(x)]1/2 = f(x)
BAf(x) = Bf2(x) = f(x)...so I thought they DO commute, but the textbook says NO! Could someone explain? Thanks!
I think you're getting lost in the symbolism. The question is asking whether
##(\sqrt{f(x)})^2 = \sqrt{(f(x))^2}##
Can you always take the square root of something?
 
  • Like
Likes terp.asessed
  • #3
Wait, you mean,
Mark44 said:
##(\sqrt{f(x)})^2 = \sqrt{(f(x))^2}##
Can you always take the square root of something?

are different? I'm sorry, but I'm confused...
 
  • #4
Well, if they're different, then the two operations aren't commutative. If you believe they are different, why are they different?

I'll ask again, can you always take the square root of something?
 
  • #5
Come to think of it, one can't square root of the function that is negative...so NOT always...
 
  • #6
terp.asessed said:
Come to think of it, one can't square root of the function that is negative...so NOT always...
Right. That's why the two operations don't commute. Good!
 
  • #7
GOTCHA----thank you!
 

1. What are Operators A and B?

Operators A and B refer to two mathematical operations that can be performed on a set of numbers or variables. These operations can include addition, subtraction, multiplication, and division.

2. What does it mean for Operators A and B to commute?

For Operators A and B to commute means that the order in which these operations are performed does not affect the end result. In other words, if we apply Operator A first and then Operator B, or vice versa, we will get the same result.

3. Why is it important for Operators A and B to commute?

The commutative property is important because it allows us to manipulate mathematical expressions more easily. It also helps us to simplify complex equations and solve problems more efficiently.

4. Are there any cases where Operators A and B do not commute?

Yes, there are cases where Operators A and B do not commute. This can occur when one of the operations is not commutative, such as division or subtraction. In these cases, the order of operations does matter and can affect the end result.

5. How can we determine if Operators A and B commute?

To determine if Operators A and B commute, we can perform a simple test by applying the operations to a set of numbers in different orders and comparing the results. If the results are the same, then the operators commute. If the results are different, then the operators do not commute.

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