Question 38 of 480
Find the equation of the locus of a point P(x,y) such that PV = PW, where V = (1,1) and W = (3,5)
- A. 2x + 2y = 9
- B. 2x + 3y = 8
- C. 2x + y = 9
- D. x + 2y = 8
Correct Answer:
D
Explanation
To find the equation of the locus of a point \( P(x,y) \) such that the distance from \( P \) to point \( V(1,1) \) is equal to the distance from \( P \) to point \( W(3,5) \), we start by using the distance formula. The distance \( d \) between two points \( (x_1, y_1) \) and \( (x_2, y_2) \) is given by:
\[
d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}
\]
### Step 1: Set up the equation
1. **Distance from \( P \) to \( V \)**:
\[
PV = \sqrt{(x - 1)^2 + (y - 1)^2}
\]
2. **Distance from \( P \) to \( W \)**:
\[
PW = \sqrt{(x - 3)^2 + (y - 5)^2}
\]
### Step 2: Set the distances equal
Since we want \( PV = PW \), we can set the two distance expressions equal to each other:
\[
\sqrt{(x - 1)^2 + (y - 1)^2} = \sqrt{(x - 3)^2 + (y - 5)^2}
\]
### Step 3: Square both sides
To eliminate the square roots, we square both sides:
\[
(x - 1)^2 + (y - 1)^2 = (x - 3)^2 + (y - 5)^2
\]
### Step 4: Expand both sides
Now we expand both sides:
- Left side:
\[
(x - 1)^2 + (y - 1)^2 = (x^2 - 2x + 1) + (y^2 - 2y + 1) = x^2 + y^2 - 2x - 2y + 2
\]
- Right side:
\[
(x - 3)^2 + (y - 5)^2 = (x^2 - 6x + 9) + (y^2 - 10y + 25) = x^2 + y^2 - 6x - 10y + 34
\]
### Step 5: Set the expanded forms equal
Now we have:
\[
x^2 + y^2 - 2x - 2y + 2 = x^2 + y^2 - 6x - 10y + 34
\]
### Step 6: Simplify the equation
Subtract \( x^2 + y^2 \) from both sides:
\[
-2x - 2y + 2 = -6x - 10y + 34
\]
Now, rearranging gives:
\[
-2x + 6x - 2y + 10y = 34 - 2
\]
This simplifies to:
\[
4x + 8y = 32
\]
### Step 7: Divide through by 4
To simplify further, divide the entire equation by 4:
\[
x + 2y = 8
\]
### Conclusion: Identify the correct option
The equation of the locus is:
\[
x + 2y = 8
\]
Thus, the correct option is **D**.
### Explanation of Other Options
- **Option A: \( 2x + 2y = 9 \)**: This does not satisfy the derived equation. If we rearranged it, we would find that it does not represent the same line as \( x + 2y = 8 \).
- **Option B: \( 2x + 3y = 8 \)**: This is a different linear equation and does not match our derived equation.
- **Option C: \( 2x + y = 9 \)**: Again, this is a different linear equation and does not represent the same relationship as \( x + 2y = 8 \).
### Revision Summary
- The locus of points equidistant from two fixed points is a straight line.
- Use the distance formula to set up the equation based on the distances to the two points.
- Square both sides to eliminate square roots, then expand and simplify.
- The final equation can be simplified to find the locus equation.
- The correct answer is \( x + 2y = 8 \) (Option D).