Question

Use slope to determine if lines AB and CD are parallel, perpendicular, or neither. A(0,2), B(5,4), C(1,8), and D(3,3). What is the slope of line CD? Enter as a ratio in its lowest terms.

Answer 1

Perpendicular, CD has a slope of -5/2

Explanation:

Parallel lines have the same slope, perpendicular have slopes that are negative reciprocals, or in other words if one slope is m then the other's slope is -1/m and if it is neither fo those then it is neither parallel or perpendicular. Also, if two lines have the same slope you have to make sure they are not the same line.

Now, to find the slope when you have two points you use the formula (y2 - y1)/(x2 - x1), where the points are (x1, y1) and (x2, y2). You can make either point point 1 or point 2. Just make sure x1 and y1 are from one point and x2 and y2 are from the other point.

So the two lines are AB and CD. Since the question asks I will start with CD. The points are (1,8) and (3,3) So I will call C point 1 and D point 2.

(y2 - y1)/(x2 - x1)

(3 - 8)/(3 - 1)

-5/2

Thankfully this is lowest terms.

Now for AB. A will be point 1 and B will be point 2

(y2 - y1)/(x2 - x1)

(4-2)/(5-0)

2/5

So they are not the same, so what if you take negative 1 over one of the slopes.

well. -1/(2/5) = -5/2

So these are perpendicular.

If you would like an explanation for how to find the full equation of a line I can explain that.