The distance of the point (1, 2) from the line x + y + 5 = 0 measured along the line parallel to 3x − y = 7 is equal to:
Step-by-Step Solution
Key Concept: Distance measured along a given direction: draw a line through the point parallel to the given line, find intersection with the target line, then compute distance.
Step 1: Identify the slope of the line parallel to the given reference line.
The line $3x - y = 7$ can be rewritten as $y = 3x - 7$, which has slope $m = 3$. Any line parallel to this will also have slope $3$.
Step 2: Write the equation of the line through point (1, 2) with slope 3.
Using the point-slope form of a line:
$$y - 2 = 3(x - 1)$$
$$y = 3x - 1$$
This is the line passing through $(1, 2)$ that is parallel to $3x - y = 7$.
Step 3: Find the intersection of this line with $x + y + 5 = 0$.
Substitute $y = 3x - 1$ into $x + y + 5 = 0$:
$$x + (3x - 1) + 5 = 0$$
$$4x + 4 = 0$$
$$x = -1$$
Substituting back to find $y$:
$$y = 3(-1) - 1 = -4$$
The intersection point is $(-1, -4)$.
Step 4: Calculate the distance from (1, 2) to (-1, -4).
Using the distance formula:
$$d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}$$
$$d = \sqrt{(-1 - 1)^2 + (-4 - 2)^2}$$
$$d = \sqrt{(-2)^2 + (-6)^2}$$
$$d = \sqrt{4 + 36}$$
$$d = \sqrt{40}$$
$$d = \sqrt{4 \cdot 10}$$
$$d = 2\sqrt{10}$$
Step 5: Simplify and match with the given options.
We can also write $\sqrt{40} = 2\sqrt{10}$. Comparing with the options provided, $\sqrt{40}$ matches **Option 3**.
**Final Answer: The distance is $\sqrt{40}$ or equivalently $2\sqrt{10}$, which corresponds to Option 3.**
Correct Answer: 4