Question

Here are Janet's steps for solving the system below by eliminating x.
2x + 3y = -1
5x + 8y = 0
Step One: Multiply the first equation by 5. 10x + 15y = -5
Step Two: Multiply the second equation by -2. -10x - 16y = 0
Step Three: Add the two equations. y = -5
Step Four: Substitute y back into the first equation. 2x + 3(-5) = -1
Step Five: Solve for x.
2x - 15 = -1
2x = 14
x = 7
Is she correct? Justify your answer. If incorrect, describe the error.

Answer 1

have a look at step 3 - is the result of adding the 2 equations correct?

Answer 2

what is +15y + (-16y) ?

Answer 3

-1

Answer 4

@cwrw238

Answer 5

well its -y

so it should be

-y = -5

which makes y = 5

right?

Answer 6

to you follow that?

Answer 7

right

Answer 8

yes

Answer 9

ok so although the rest of the math is correct the value of x cannot be 7 because y is not = -5

can you find the correct value of x ?

Answer 10

i'll start you ogg

2x + 3(5) = -1

Answer 11

*off lol!

Answer 12

ok

Answer 13

haha i figured so

Answer 14

honestly im not very experienced on this

Answer 15

2x + 15 = -1
the aim is to get the terms in x on one side of the '=' and numbers on the right
first subtract 15 from both sides:

2x + 15 - 15 = -1 - 15 (15 - 15 is of course = 0) so

2x = -16
now divide both sides by 2 to find x

2x /2 = -16/2

x = -8

Answer 16

and y=5

Answer 17

so shes incorrect

Answer 18

yes

Answer 19

sweet, thank you for the help :)

Answer 20

there is only one mistake - step 3
but this makes both values wrong

Answer 21

yw