Question

Choose the system of equations that matches the following graph:

https://lss.brainhoney.com/Resource/22181743,AD2,0,C,3,0/Assets/72257_53b5b170/02_13_mod_2_test_bankg_23.gif

Answer 1

A. 5x + 2y = –14
7x + y = 7

B. 5x + 2y = –14
7x – y = 7

C. 5x – 2y = –14
7x + y = 7

D. 5x – 2y = –14
7x – y = 7

Answer 2

is that the whole picture?

Answer 3

yeah

Answer 4

@amistre64 Can you check my answer? I think it's D

Answer 5

looks right

Answer 6

Plug in (0,-7) into the equations and see for which answer choice does it work in both equations.

Answer 7

Yeah ok that's what I did and I got D. Thanks! :)

Answer 8

keep in mind that there are many lines that can pass thru that point; so plugging in might not be a sufficient measure in this case.

Answer 9

@TheSmartOne wait so I can't plug in to find the answer? Is D right?

Answer 10

D is wrong.

Answer 11

@amistre64 There are two lines and they both intersect at (0,-7) so plugging in that point to test which 2 lines in the answer choices work it the logical way to solve it.

Answer 12

Or you can graph the two lines in each answer choice, but that would take longer.

Answer 13

how do we know they gave the equations of the 2 lines correctly? after all, each option has a different setup.

Answer 14

suppose we are given

y = L1 and y=L2 in one option

then

y = L'1 and y=L2 in another

since they all have a common point, the point satisfies both options

Answer 15

They graphed the two lines and asked us what are the two lines :P

Answer 16

yes, but not all the options define the lines correctly; but some option MIGHT give us a setup where more than one option is true for a given point.

Answer 17

in this case: plugging in MIGHT not work out if we dont know the equation of the lines to start with

Answer 18

I think it would be good if you changed the equations to y=mx+b and check with this website: https://www.desmos.com/calculator to make sure. Or if you have a graphic calculator with you, you can graph them there.

Answer 19

You don't even need to change it in the format of y=mx+b

It still graphs it as the equation is already :P

Answer 20

spose L1 and L2 are given,we know they have a common point for a solution

we also know that for some ungraphed line L'1, we have the same solution

option A: y=L1 and y=L2
option B: y=L'1 and y=L2

we plug in the common point, and both options seem valid, but unless we know the properties of the lines we cant know for certain which is valid by just plugging in the common point.

Answer 21

now, if only one option gives a true solution, then yeah, its that one :) but im just demonstrating that plugging in is not always the best option here.

Answer 22

lets give option C: y=L1 and y=L'1

this also satisfies the common point .... now all 3 options seem equally valid.

Answer 23

oh, i mistype and said D worked didnt i ..... my brain said one thing my fingers typed another . hence the diatribe lol

Answer 24

@amistre64 So it is D?

Answer 25

You seem to only want the final answer.

Answer 26

And D is wrong.

Answer 27

Oh...but @amistre64 said it was right?

Answer 28

5x + 2y = –14
7x + y = 7

@amistre64 is this the answer?

Answer 29

"oh, i mistype and said D worked didnt i"
~Amistre64

Answer 30

5x + 2y = –14
7x + y = 7 so is this the answer?

Answer 31

Nope.

Answer 32

5x – 2y = –14
7x + y = 7 ?

Answer 33

So we are just going to guess?

Answer 34

How did you arrive to the answer being D?