Question

What is the equation of the line that is perpendicular to -x + y = 7 and passes through (-1, -1)?


A) -x + y = 2
B) -x – y = 2
C) x – y = 2
D) -x – y = 0
E) x + y = 0

Answer 1

The first thing you need to do here is find the slope of the line you have. To do this you need to get it into slope-intercept form: y = mx + b, where m is the slope and b is the y-intercept. Doing this you get y = x + 7. What is the slope of the line y = x + 7?

Answer 2

0?

Answer 3

if you are just stuck with a variable. like x, it is not written but it is there...it is 1x.
x is the same as 1x...y is the same as 1y.
So your slope of y = x + 7...which is the same as y = 1x + 7...making your slope 1
understand ?

Answer 4

yes, thank you! I just don't undersand where to go from here!

Answer 5

now that we have the slope, we will continue. A perpendicular line will have a negative reciprocal slope. All that means is " flip " the slope, and change the sign.
Slope = 1, or 1/1...so we flip the slope and change the sign, making our slope be -1.
Have I lost you ?

Answer 6

nope, I still understand!

Answer 7

now we will use y = mx + b
slope(m) = -1
(-1,-1)..x = -1 and y = -1
now we sub
-1 = -1(-1) + b
-1 = 1 + b
-1 - 1 = b
-2 = b

so our perpendicular line is : y = -x - 2...but it seems we need it in standard form Ax + By = C

y = -x - 2 --- add x to both sides
x + y = -2
hmmm..not an answer choice
x + y = -2 --->(-1)
-x - y = 2...well, that works

Answer 8

thank you so soo much!!!

Answer 9

no problem :)