Question 24 of 480
If m∗n=(mn−nm) for m, n belong to R, evaluate -3*4
- A.
−25
12
−
25
12
- B.
−7
12
−
7
12
- C.
7
12
7
12
- D.
25
12
25
12
Correct Answer:
C
Explanation
To solve the problem, we need to evaluate the expression given by the formula:
\[
m * n = \left( \frac{m}{n} - \frac{n}{m} \right)
\]
where \( m \) and \( n \) are real numbers. In this case, we are asked to evaluate \( -3 * 4 \).
### Step 1: Identify the values of \( m \) and \( n \)
Here, we have:
- \( m = -3 \)
- \( n = 4 \)
### Step 2: Substitute the values into the formula
Now, we substitute \( m \) and \( n \) into the formula:
\[
-3 * 4 = \left( \frac{-3}{4} - \frac{4}{-3} \right)
\]
### Step 3: Calculate each fraction
1. Calculate \( \frac{-3}{4} \):
\[
\frac{-3}{4} = -0.75
\]
2. Calculate \( \frac{4}{-3} \):
\[
\frac{4}{-3} = -\frac{4}{3} \approx -1.3333
\]
### Step 4: Combine the fractions
Now we need to combine these two fractions:
\[
-3 * 4 = \left( -\frac{3}{4} - \left(-\frac{4}{3}\right) \right) = -\frac{3}{4} + \frac{4}{3}
\]
### Step 5: Find a common denominator
To add these fractions, we need a common denominator. The least common multiple of 4 and 3 is 12.
- Convert \( -\frac{3}{4} \) to a fraction with a denominator of 12:
\[
-\frac{3}{4} = -\frac{3 \times 3}{4 \times 3} = -\frac{9}{12}
\]
- Convert \( \frac{4}{3} \) to a fraction with a denominator of 12:
\[
\frac{4}{3} = \frac{4 \times 4}{3 \times 4} = \frac{16}{12}
\]
### Step 6: Add the fractions
Now we can add the two fractions:
\[
-\frac{9}{12} + \frac{16}{12} = \frac{16 - 9}{12} = \frac{7}{12}
\]
### Final Answer
Thus, the evaluation of \( -3 * 4 \) is:
\[
-3 * 4 = \frac{7}{12}
\]
### Conclusion
The correct option is **C. \( \frac{7}{12} \)**.
### Explanation of Other Options
- **Option A: \( -\frac{25}{12} \)**: This option is incorrect because it does not reflect the correct calculation of the fractions involved.
- **Option B: \( -\frac{7}{12} \)**: This option is incorrect as it has the wrong sign; our calculation resulted in a positive value.
- **Option D: \( \frac{25}{12} \)**: This option is also incorrect as it does not match our calculated result.
### Revision Summary
- The operation defined is \( m * n = \left( \frac{m}{n} - \frac{n}{m} \right) \).
- Substitute the values of \( m \) and \( n \) into the formula.
- Convert fractions to a common denominator to perform addition.
- The final result for \( -3 * 4 \) is \( \frac{7}{12} \).