Question

Elimination using multiplication heeelllp

7x+4y=-4
5x+8y=28

Answer 1

what's the question here....

Answer 2

How do I solve this by elimination using multiplication

Answer 3

7x+4y=-4 solve for y

Answer 4

How though

Answer 5

7x+4y=-4
5x+8y=28

Multiply the first equation by 2 so that way we can eliminate y.

For example

if the equation is a + b = c

If we multiply both sides by 2, we get:

2(a + b) = 2(c)

2a + 2b = 2c

Do that for 7x+4y=-4. Multiply it by 2 on both sides

Answer 6

I now have 14x+4y=-8

Answer 7

A little mistake:

Distributive property on the left side

2(7x + 4y) = 2(7x) + 2(4y)
= 14x + 8y

So the equation should be:

14x + 8y = -8

Do you understand? :)

Answer 8

Yea

Answer 9

So let's put this new equation next to the second equation

14x + 8y = -8
5x + 8y = 28

Now, subtract the second equation from the first

14x - 5x + 8y - 8y = -8 - 28

Simplify that further :)

Answer 10

Would it be -36 or 9

Answer 11

Custom I have 9x=-20 sorry I mentioned to say -20 instead of 9

Answer 12

Because not custom

Answer 13

-36 was correct. And so is 9

-8 - 28

That's the same thing as

-1(8 + 28) = -1(36) = -36

and so now we have

9x = -36

Divide both sides by 9 to solve for x

Answer 14

X=4?

Answer 15

@TheSmartOne

Answer 16

-36/ 4 = ?

There is a negative sign. Be careful!

Answer 17

Sorry forgot to put it in

Answer 18

No how do I find y

Answer 19

Now not no

Answer 20

@TheSmartOne

Answer 21

Plug in the value of x into any of the equations and solve for y.

7(-9) +4y=-4

Solve for y

Answer 22

Why a negative 9

Answer 23

Never mind

Answer 24

Now I have -14+4y=-4

Answer 25

my bad it should be -4

Answer 26

So it's not what I got

Answer 27

7(-4) +4y=-4

Solve for y

Answer 28

I now have -28+4y=-4

Answer 29

Add 28 to both sides now :)

Answer 30

4y=24?

Answer 31

Good, good!

Now divide both sides by 4

Answer 32

Y=6?

Answer 33

That's correct!

And so we got:

x = -4
y = 6

That makes the final solution in coordinate form

(-4, 6)

Because coordinate form is (x, y)

Answer 34

Thanks do you mind helping me with 1 more please?

Answer 35

Sure! Since I just explained it to you, I want you to try this one on your own. Post all your work and I'll try to catch your mistakes/help you along the way :)

Answer 36

Well the problem is sorta different because it's
2x-4y=-22
3x+3y=30

Answer 37

Ah, it's not that different.

We need to multiply the first equation by a certain number, and the second equation by a different number so that way we can get the same number like 6x in both the first and second equation.

So, which variable do you want to eliminate?

Answer 38

Can we eliminate 3y

Answer 39

ok

We have 4y in the first equation, and 3y in the second equation

Can you find the least common multiply of 4 and 3?

Answer 40

Is it 1?

Answer 41

List the multiples.

For example, multiples of 2 are: 2, 4, 6, 8, 10, and so on

Answer 42

12 right?

Answer 43

I forgot to put the 2 in 12 sorry

Answer 44

Correct

2x-4y=-22
3x+3y=30

That means we need to multiply the first equation by 3, and the second equation by 4

Answer 45

All of it or just the 2x-4y parts

Answer 46

You multiply both sides

and remember

a(b + c) = ab + ac
a(b - c) = ab - ac

Answer 47

6x-12y=66?
12+12y=120?

Answer 48

@TheSmartOne

Answer 49

6x - 12y = -66
12x + 12y = 120

You forgot the - sign before 66, I've added it :P

Not add both equations:

6x + 12x - 12y + 12y = -66 + 120

The y's should cancel, and simplify it more :)

Answer 50

BRB I have to clean

Answer 51

Sure!