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Section 14.3: Let's look at problem #37. [The following lists the steps a student uses to solve a system of equations, but an error has been made. Find and describe the error and correct the answer.
3x - y = _4
2x + y = 16
5x = 20
x = 4
3x - y = 4
3(4) - y = 4
y = 4 - 12
y = -8

2006-09-29 05:30:56 · 6 answers · asked by Anonymous in Education & Reference Homework Help

6 answers

5x=12
x=2.4
4.8+y=16
y=11.2
(2.4,11.2}

2006-09-29 05:34:01 · answer #1 · answered by raj 7 · 0 0

The first part of the problem is done correctly as long as there isn't supposed to be anything in front of the 4 in the first equation.

In the second part when the student did substitution they got this equation:
3(4) - y = 4
This becomes
12 - y = 4
Then you have to subtract 12 from both sides leaving our equation to look like:
-y = 4 - 12

The mistake that I saw was that the student dropped the negative in front of the y variable. Now you get to figure out what the real value of y should be.

Hope this helps. Good Luck.

2006-09-29 12:44:04 · answer #2 · answered by SmileyGirl 4 · 0 0

Take a look at the last three steps:

3(4) - y = 4
y = 4 - 12
y = -8

What it should have been was:

3(4) - y = 4
-y = 4 - 12
-y = -8
y = 8

The mistake was turning the neg. y to a pos. y. When you isolate a variable, it must keep it's pos. or neg. value. Then you can just divide both sides by -1 to get a positive variable.

2006-09-29 12:52:14 · answer #3 · answered by Anonymous · 0 0

Here is the solution: (Pointing out the mistakes made)

First step (given):

Second Step (given)

3rd step is wrong

In addition, a mistake is made.

5x = (-4 + 16) = 12 ( & not 20)

So x = 12 / 5 = 2.4.

So 4th step (x= 4) is WRONG.

5th step is Given. It is wrong. 3x - y = = - 4 ( & not + 4)

6th step: substitution of the value of x as 4 is wrong. It must be 2.4

7th step of finding the value of 'y' is wrong.

It must be y = 11.2

Reason: 3 (2.4) - y = -4
+. 7.2 - y = -4
=> -y = -11.2
y = 11.2

Answer: x= 2.4 & y = 11.2.

2006-09-29 12:35:18 · answer #4 · answered by Anonymous · 0 1

You forgot the negative sign in front of "y" so your answer should read "-y = - 8"; therefore y = 8.

2006-09-29 12:41:05 · answer #5 · answered by dmspartan2000 5 · 1 0

stop making us do your home work and do it yourself

By the way the answer is y=-5 not y=-8

2006-10-01 21:02:47 · answer #6 · answered by Anonymous · 0 0

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