High School

If the straight line [tex]L_1[/tex] passes through the points [tex](3,1)[/tex] and [tex](2, k)[/tex], and the straight line [tex]L_2[/tex] makes an angle of measure [tex]45^\circ[/tex] with the positive direction of the [tex]x[/tex]-axis, find the value of [tex]k[/tex] if:

1. [tex]L_1 \perp L_2[/tex]
2. [tex]L_1 \parallel L_2[/tex]

Answer :

Sure! Let's solve this problem step by step.

### Part 1: [tex]\(L_1 \perp L_2\)[/tex]

1. Find the Slope of [tex]\(L_2\)[/tex]:
- [tex]\(L_2\)[/tex] makes an angle of 450 degrees with the positive x-axis. Since angles are typically measured between [tex]\(0^\circ\)[/tex] and [tex]\(360^\circ\)[/tex], we should convert 450 degrees by subtracting 360. This gives us [tex]\(450^\circ - 360^\circ = 90^\circ\)[/tex].
- An angle of 90 degrees indicates a vertical line, which means the slope of [tex]\(L_2\)[/tex] is undefined.

2. Perpendicular Condition:
- For two lines to be perpendicular, the product of their slopes should be [tex]\(-1\)[/tex]. However, since the slope of [tex]\(L_2\)[/tex] is undefined, the slope of [tex]\(L_1\)[/tex] must be 0, which means [tex]\(L_1\)[/tex] is a horizontal line.

3. Finding [tex]\(k\)[/tex] for Perpendicular Lines:
- The slope of a horizontal line [tex]\(L_1\)[/tex] is 0. This means the difference in y-coordinates must be zero: [tex]\((k - 1) = 0\)[/tex].
- Therefore, [tex]\(k = 1\)[/tex].

### Part 2: [tex]\(L_1 // L_2\)[/tex]

1. Find the Slope of [tex]\(L_2\)[/tex]:
- As established above, [tex]\(L_2\)[/tex] is a vertical line, with an undefined slope.

2. Parallel Condition:
- For lines to be parallel, they must have the same slope. But since a vertical line has an undefined slope, [tex]\(L_1\)[/tex] cannot have a defined slope if it were to be parallel.
- A horizontal line and a vertical line cannot be parallel. Therefore, there is no value of [tex]\(k\)[/tex] that would make [tex]\(L_1\)[/tex] parallel to [tex]\(L_2\)[/tex].

In summary:
- If [tex]\(L_1\)[/tex] is perpendicular to [tex]\(L_2\)[/tex], then [tex]\(k = 1\)[/tex].
- If [tex]\(L_1\)[/tex] is parallel to [tex]\(L_2\)[/tex], there is no solution (no such value of [tex]\(k\)[/tex]).