Question

How do you solve 2x + y = 7 x – y = –4?

2x + y = 7

x – y = –4

a. (1,-5)

b. (1,5)

c.(-1,-5)

d.(-1,5)

Anything is appreciated

Answers

Add .. its like elimination .. i'll show you the steps its pretty self explanitory(:

2x + y = 7

x - y = -4

Okay this ones easy .. first y and - y cancel out

2x = 7

x = -4

Add

3x = 3

Now solve for x

so

x = 1

You got that from dividing each side by 3

So now you can eliminate c and d because they have -1 as x not 1

Now you pug x=1 in one of the equations i'll show you both

(1) - y = -4

-1 -1

-y=-5

Then you divide both sides by negative 1 because there is always a 1 or negative 1 infront of a variable

y=5

so your answer is b

if you wanted to plug in x=1 to the 2x + y= 7 it would come out the same.. this is what your work would be

2(1) + y = 7

2 + y = 7

-2 -2

y=5

See same thing!

heres how you can check (you can also do this with all the answers and kind of work backwords .. if you ever forget the write way .. it will only work on multible choice)

Check

2(1) + 5 = 7

2 + 5 =7

7 = 7

Good!

(1) - (5) = -4

-4=-4

Good!

There ya go(:

#1

Hi,

Add.

2x + y = 7

x – y = –4

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

3x = 3

x = 1

If x = 1 and 2x + y = 7, then:

2(1) + y = 7

2 + y = 7

y = 5

(1,5) <==ANSWER B

I hope that helps! :-)

#2

Start with the second equation x-y=-4

add y to both sides, forming x=y-4

plug that equation in for x in the first equation

2(y-4)+y=7. distribute

2y-8+y=7. collect like terms

3y-8=7. add 8 to both sides

3y=15. divide both sides by 3

y=5

plug 5 for y in the second equation

x-5=-4 add 5 to both sides

x=1

your answer in coordinates would be (1,5) which is (b)

EDIT: I swear I just helped you with a similar equation...

#3