## marird15 2 years ago How can u tell whether these lines are parallel or perpendicular or neither with out graphing? line 1; through (-1,9) and (-6,-6) line 2; through (-7,-23) and (0,-2)

1. RyanL.

(-1,9) and (-6,-6) : slope =3 (-7,-23) and (0,-2): slope=3 same slope means lines are parallel

2. marird15

how did you figure that out with out graphing?

3. hartnn

there is a formula to find the slope of line with 2 points given....

They calculated the slope of each line using $\Delta y \over \Delta x$ When the slopes are equal to each other (in this case they were both 3) they are parallel. If they were negative reciprocals like one was 3 and the other -1/3. then they would of been perpendicular.

5. hartnn

for perpendicular,slopes must be negative inverse

6. RyanL.

@radar I used that method....sorry for nothing showing my work.

7. marird15

ohhhh. okay i got it. and its okay @RyanL.

@RyanL, good work, I was just trying to assist. I want to explain what a negative reciprocal is, because by the questions being submitted he is going to need to understand that too.

9. marird15

**She

One number is a negative reciprocal of another number if their product is -1.