Question 55 of 480
A binary operation * is defined by a * b = a\(^b\). If a * 2 = 2 - a, find the possible values of a.
- A. 1, -1
- B. 1, 2
- C. 2, -2
- D. 1, -2
Correct Answer:
D
Explanation
To solve the problem, we need to analyze the binary operation defined by \( a * b = a^b \) and the equation given, \( a * 2 = 2 - a \). Let's break this down step-by-step.
### Step 1: Understand the Binary Operation
The operation \( a * b \) is defined as \( a^b \). This means that when we see \( a * 2 \), it translates to \( a^2 \).
### Step 2: Set Up the Equation
From the problem, we have:
\[
a * 2 = 2 - a
\]
Substituting the definition of the operation, we get:
\[
a^2 = 2 - a
\]
### Step 3: Rearranging the Equation
To solve for \( a \), we need to rearrange the equation:
\[
a^2 + a - 2 = 0
\]
This is a standard quadratic equation in the form \( ax^2 + bx + c = 0 \), where \( a = 1 \), \( b = 1 \), and \( c = -2 \).
### Step 4: Factor the Quadratic
Next, we can factor the quadratic equation:
\[
(a + 2)(a - 1) = 0
\]
This gives us two possible solutions:
1. \( a + 2 = 0 \) → \( a = -2 \)
2. \( a - 1 = 0 \) → \( a = 1 \)
### Step 5: List the Possible Values
Thus, the possible values of \( a \) are:
\[
a = 1 \quad \text{and} \quad a = -2
\]
### Step 6: Verify the Solutions
To ensure these values are correct, we can substitute them back into the original equation \( a * 2 = 2 - a \):
1. For \( a = 1 \):
\[
1 * 2 = 1^2 = 1
\]
\[
2 - 1 = 1
\]
Both sides are equal, so \( a = 1 \) is a valid solution.
2. For \( a = -2 \):
\[
-2 * 2 = (-2)^2 = 4
\]
\[
2 - (-2) = 2 + 2 = 4
\]
Both sides are equal, so \( a = -2 \) is also a valid solution.
### Step 7: Evaluate the Options
Now, let's look at the options provided:
- **A. 1, -1**: Incorrect because -1 is not a solution.
- **B. 1, 2**: Incorrect because 2 is not a solution.
- **C. 2, -2**: Incorrect because 2 is not a solution.
- **D. 1, -2**: Correct because both 1 and -2 are valid solutions.
### Summary of the Solution
- The binary operation is defined as \( a * b = a^b \).
- We set up the equation \( a^2 = 2 - a \) and rearranged it to \( a^2 + a - 2 = 0 \).
- Factoring gives us the solutions \( a = 1 \) and \( a = -2 \).
- The correct answer is option D: 1, -2.
### Revision Summary
- Understand the definition of the binary operation \( a * b = a^b \).
- Rearrange the equation to form a standard quadratic equation.
- Factor the quadratic to find possible values of \( a \).
- Verify solutions by substituting back into the original equation.