Question

What is the solution of the system?
4x - 4y = -40
-4x + 7y = 55

(–5, –5)
(5, 5)
(5, –5)
(–5, 5)

Answer 1

What method for solving systems of equations do you know?

Answer 2

i dont really know a method.. like i tried to turn 4x - 4y = -40 into 4x + 40/4 but it doesnt work

Answer 3

Elimination would be a good way to do this one. So basically add together the two equations.

Answer 4

@Acoustics95 first add both the equation u will get the value of y
then put value of y in one of the equation given above u will get the required value of x

Answer 5

how would i add the equations?

Answer 6

Do it one piece at a time
so 4x + -4x to start

Answer 7

so x

Answer 8

Almost, what is 4 - 4?

Answer 9

0?

Answer 10

so that would leave an x right?

Answer 11

yes so you would have 0x, which is just 0.

Answer 12

ohhh

Answer 13

now do the next pieces
-4y + 7y

Answer 14

3y

Answer 15

ok, now what about the two items on the right sides of the =

Answer 16

15?

Answer 17

good
so now you have 3y=15, can you solve for y?

Answer 18

5

Answer 19

good!
now plug y=5 into one of the equations to solve for x

Answer 20

4x - 20 = -40?

Answer 21

good, keep going

Answer 22

-4x + 30 = 55

Answer 23

well you only have to use one of the equations to find x.
so choose one to use your solving equation steps to find what x=

Answer 24

so on the first equation the first 4x = -20?

Answer 25

@rachelfreak123 ?

Answer 26

yeah, now one more step to get the value

Answer 27

whats the last step?

Answer 28

divide both sides

Answer 29

by -20?

Answer 30

no, by the number in front of the x

Answer 31

to the answer is (5, 5)?

Answer 32

so*

Answer 33

almost, you have 4x=-20, check your sign for x.

Answer 34

oh so its 4/-20 so (5, -5)?

Answer 35

well...... the x is negative, so remember that the values are in the order (x, y)

Answer 36

im so confused.. :/

Answer 37

well you know that the y=5 right?
and the x=-5, so you just have to make srue you put it in the ( ) in the correct order

Answer 38

4x = -20

4x/4 = -20/4

4/4 is 1 so that is
x= -20/4

-20 divided by 4 is -5

x= -5

Answer 39

ohhhhhhh so its (-5, 5)

Answer 40

There you go!

Answer 41

i see i mixed the places

Answer 42

thank you very much!

Answer 43

Welcome