Question

Write the equation of the line given by the following graph in standard form.


2x – y = –1

2x + y = –1

2x + y = 1

2x – y = 1

Answer 1

identify two points that lie on that line

Answer 2

then plug each point into each answer choice

if both points make the equation true, then the equation is the answer

Answer 3

what are the two points

Answer 4

one point is (0,1)

what's another?

Answer 5

no idea

Answer 6

im terrible at this

Answer 7

how about (1,-1)

see how I'm getting these two points?

Answer 8

and that's ok, that's why there's practice

Answer 9

yes i do

Answer 10

ok so let's just focus on (0,1) for now

Answer 11

alrighty

Answer 12

if we plug it into choice A, then we get

2x – y = –1

2(0) – 1 = –1 ... replace x with 0 and y with 1

0 - 1 = -1

-1 = -1

so that's true

This means that (0,1) is definitely on 2x – y = –1

Answer 13

alright cool

Answer 14

now let's focus on (1,-1)

plug it into choice A to get

2x – y = –1

2(1) – (-1) = –1 .. plug in x = 1 and y = -1

2 + 1 = -1

3 = -1

this is false, so (1,-1) is NOT on the line 2x – y = –1

Answer 15

so 2x – y = –1 goes through (0,1) but it does NOT go through (1,-1)

Answer 16

so A is incorrect

Answer 17

yep, it needs to go through both points to work

Answer 18

alright so B

Answer 19

what do you get when you plug in (0,1) into the equation for choice B?

Answer 20

2x + y = -1
2 (0) + 1 = -1
0 + 1 = -1
1 = -1
so that is incorrect

Answer 21

right?

Answer 22

very good

Answer 23

that rules out B

Answer 24

so the answer is C

Answer 25

(0,1) works because

2x + y = 1

2(0) + 1 = 1

0 + 1 = 1

1 = 1

is true

------------------

let's check out (1,-1)

2x + y = 1

2(1) + (-1) = 1

2 - 1 = 1

1 = 1

and that works too

both points are confirmed to be on this line, so 2x + y = 1 is definitely the answer

Answer 26

yay thank you!!

Answer 27

you're welcome