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

@texaschic101

Answer 2

haha,as soon as i mention you

Answer 3

Look at step 3, do you notice anything?

Answer 4

shouldnt it be y=5

Answer 5

Yeah :)

Answer 6

yeshh

Answer 7

So you can see from step 3 and onwards, the whole problem will be wrong then.

Answer 8

2x + 3y = -1 --->(5)
5x + 8y = 0 --->(-2)
---------------------
10x + 15y = -5 (result f multiplying by 5)
-10x - 16y = 0 (result of multiplying by -2)
--------------------add
-y = -5
y = 5 (This is where Janet made her mistake)

now sub 5 in for y in either equation to find x
2x + 3y = -1
2x + 3(5) = -1
2x + 15 = -1
2x = -15 - 1
2x = -16
x = -8

check..
2x + 3y = -1
2(-8) + 3(5) = -1
-16 + 15 = -1
-1 = -1 (correct)

x = -8 and y = 5 and Janet is incorrect

Answer 9

thank you again miss texas, youre a life saver

Answer 10

well...I don't know about a lifesaver...but thank you :)

Answer 11

pretty close