Question

Solve the following system of equations graphically, find the graph

2x -y = -1

x + y = -2

Answer 1

2?

Answer 2

Easiest way to do this is to plug in the point of intersection and if both equations are true, then it's the correct answer. For instance, let's check 2.
\[2x - y = -1\]\[2(1) - (-1) = -1\]\[2 + 1 = -1\]\[3 ≠ -1\]THerefore, it isn't 2.

Answer 3

i was talking about the graph...

Answer 4

Also, if the point of intersection is the same in two choices, then you have to make sure the lines make sense.

Answer 5

And yes, 2 is incorrect since the solution set is also the point of intersection when graphed...

Answer 6

how about 3?..

Answer 7

Are you just guessing at this point?

Answer 8

no i'm asking if you can help me solve it...

Answer 9

Alright. I explained the process above...
Let's take a look at choice 3...
2x - y = -1
Plus in the point of intersection, (-1, 1)
2(-1) - (1) = -1
-2 - 1 = -1
-3 ≠ -1
Do you see how the final equations ends up false since -3 does NOT equal -1?

Answer 10

ok. and choice 1,
(-1, -1)
2(-1)-(-1)=-1

Answer 11

-1+-1=2

Answer 12

so it is choice 1..

Answer 13

thank you...

Answer 14

my idea would be to use a knowledge of the equations to match the graph in this manner

x + y = -2 notice this is pretty easy to turn to y = mx+b format

y = -x-2

we need to find an option that has a line going thru y=-2 and a downill slope of -1

Answer 15

Um...
\[2(-1) - (-1) = -1\]\[-2 + 1 = -1\]\[-1 = -1\]You should always check both equations by the way for the future, but it is indeed choice 1 :)

Answer 16

oh, ok sorry.. thanks again...

Answer 17

1 and 3 fit the thru -2 part; and 3 is too steep for comfort

Answer 18

A plot is attached.