Prove that A is idempotent if and only if A' is idempotent. Getting Started: The phrase "if and only if" means that you have to prove two statemen 1. If A is idempotent, then A' is idempotent. 2. If AT is idempotent, then A is idempotent. STEP 1: Begin your proof of the first statement by assuming that A is idempotent. This means that A STEP 2: Take the transpose of both sides of the equation from Step 1. T STEP 3: Use the properties of the transpose to simplify your result from Step 2. T This shows that A' is idempotent. STEP 4: Begin your proof of the second statement by assuming that A is idempotent. This means that A' = STEP 5: Take the transpose of both sides of the equation from Step 4. STEP 6: Use the properties of the transpose to simplify your result from Step 5. %3D This shows that A is idempotent.

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## Prove that \( A \) is idempotent if and only if \( A^T \) is idempotent.

### Getting Started:
The phrase "if and only if" means that you have to prove two statements.

1. If \( A \) is idempotent, then \( A^T \) is idempotent.
2. If \( A^T \) is idempotent, then \( A \) is idempotent.

### STEP 1: 
Begin your proof of the first statement by assuming that \( A \) is idempotent. This means that
\[ A^2 = \boxed{A}. \]

### STEP 2: 
Take the transpose of both sides of the equation from Step 1.
\[ (A^2)^T = A^T. \]

### STEP 3: 
Use the properties of the transpose to simplify your result from Step 2.
\[ (A \cdot A)^T = A^T \]
\[ A^T \cdot (A^T)^T = A^T \]
\[ A^T \cdot A^T = A^T \]

This shows that \( A^T \) is idempotent.

### STEP 4: 
Begin your proof of the second statement by assuming that \( A^T \) is idempotent. This means that
\[ (A^T)^2 = \boxed{A^T}. \]

### STEP 5: 
Take the transpose of both sides of the equation from Step 4.
\[ [(A^T)^2]^T = (A^T)^T. \]

### STEP 6: 
Use the properties of the transpose to simplify your result from Step 5.
\[ [A^T \cdot A^T]^T = (A^T)^T \]
\[ (A^T)^T \cdot A^T = A \]
\[ A \cdot A = A \]

This shows that \( A \) is idempotent.

By completing these steps, we have shown that \( A \) is idempotent if and only if \( A^T \) is idempotent.
Transcribed Image Text:## Prove that \( A \) is idempotent if and only if \( A^T \) is idempotent. ### Getting Started: The phrase "if and only if" means that you have to prove two statements. 1. If \( A \) is idempotent, then \( A^T \) is idempotent. 2. If \( A^T \) is idempotent, then \( A \) is idempotent. ### STEP 1: Begin your proof of the first statement by assuming that \( A \) is idempotent. This means that \[ A^2 = \boxed{A}. \] ### STEP 2: Take the transpose of both sides of the equation from Step 1. \[ (A^2)^T = A^T. \] ### STEP 3: Use the properties of the transpose to simplify your result from Step 2. \[ (A \cdot A)^T = A^T \] \[ A^T \cdot (A^T)^T = A^T \] \[ A^T \cdot A^T = A^T \] This shows that \( A^T \) is idempotent. ### STEP 4: Begin your proof of the second statement by assuming that \( A^T \) is idempotent. This means that \[ (A^T)^2 = \boxed{A^T}. \] ### STEP 5: Take the transpose of both sides of the equation from Step 4. \[ [(A^T)^2]^T = (A^T)^T. \] ### STEP 6: Use the properties of the transpose to simplify your result from Step 5. \[ [A^T \cdot A^T]^T = (A^T)^T \] \[ (A^T)^T \cdot A^T = A \] \[ A \cdot A = A \] This shows that \( A \) is idempotent. By completing these steps, we have shown that \( A \) is idempotent if and only if \( A^T \) is idempotent.
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