Explain this Algebra problem to me PLEASE!!

[StaceyinLA]

Solve the equation. Make sure you simplify before starting to undo.

2-7(4-x)=9

Someone please explain this backwards undoing stuff. I do NOT remember working problems this way in HS Algebra.

[8FillTheHeart]

Solve the equation. Make sure you simplify before starting to undo.

2-7(4-x)=9

Someone please explain this backwards undoing stuff. I do NOT remember working problems this way in HS Algebra.

This is an order of operations problem. The first thing you need to do distribute -7 across the (4-x). The problem then becomes

2-28+7x=9

Now simply solve by adding 26 to both sides.

7x=35

divide both sides by 7

x=5

[Pam L in Mid Tenn]

I think undoing is another word for "solve for x".

I would work the equation by distributing the 7 to the 4 and then the x.

It would look like:

2 - (7)(4) - (7)(x) = 9

Then multiply, combine like terms, and solve for x.

I am not a math person, but I think that is correct.

[StaceyinLA]

but ds said that's not how he was taught. However, I am still totally confused. I HATE Algebra!!!

[Dana]

See if this (http://www.purplemath.com/modules/solvelin2.htm)helps.

I really like this site for explanations.

[jennifermarie]

Maybe he was taught this way:

2-7(4-x)=9
subtract 2=
-7(4-x)=7
divide by -7=
4-x=-1
subtract 4=
-x=-5
divide by -1=
x=5

[StaceyinLA]

Gosh I don't know if I like TT at ALL!!! I really wanted it to work because I'm so math-challenged (well, Algebra challenged; I'm great with actual numbers and do bookkeeping part-time).

Anyway, I'm rethinking this whole thing...

[stacim]

Based on the instructions, I would work the problem as the first two posters did. However, it can also be worked as jennifermarie did. Both will get you the same answer. There isn't only one way to solve equations, but some ways make it easier.

Does the second method match what he has learned? If not, can you have him show us how he would work it?

[StaceyinLA]

he said it was more like what jennifermarie posted. He didn't agree with me when I suggested multiplying the 7 by the numbers in the parentheses.

Anyway, I'm just totally frustrated with the working in reverse stuff (undoing). I do not ever remember learning this!

[8FillTheHeart]

he said it was more like what jennifermarie posted. He didn't agree with me when I suggested multiplying the 7 by the numbers in the parentheses.

Anyway, I'm just totally frustrated with the working in reverse stuff (undoing). I do not ever remember learning this!

While jennifermarie's method works, I wouldn't teach it that way b/c order of operations would require the distribution of multiplication prior to adding/subtracting, not to mention it is simply a more complicated process than to simplify on one side of the equation prior to working on both sides of the equation.

ETA: Of course, it is as simple as.......as long as you do the same operation on both sides of the equation, the equation remains equal.

[transientChris]

Here is what I did to explain it very carefully.
Original 2-7(4-x)= 9
subtraction means adding the neg 2+ -7(4 -x) = 9
Multiply -7 by 4 and -x 2-28+7x=9
add the 2 and -28 -26+7x=9
add 26 to both sides 7x=35
divide both sides by 7 x=5

[fractalgal]

Solve the equation. Make sure you simplify before starting to undo.

2-7(4-x)=9

Someone please explain this backwards undoing stuff. I do NOT remember working problems this way in HS Algebra.

There are multiple ways to solve this problem.

I would first rewrite it:
2 + -7(4 + -x) = 9 Rewrite the subtraction as the addition of the opposite number. This makes it easier to distribute the -7 and will cause less confusion with the signs.

One way:
-7 (4 + -x) = 7 ( I subtracted 2 from both sides.)

1. Divide both sides by - 7
then you have (4 + -x) = -1

2. Add x to both sides: 4= x-1

3. Then you have x = 5.

The second way:

2 + -28 + 7x = 9 Distribution of multiplication over addition

-28 + 7x = 7 Subtract 2 from both sides.

7x = 35 Add 28 to both sides

x = 5

I slightly prefer the second way, but both methods work equally well.

[angela in ohio]

Solve the equation. Make sure you simplify before starting to undo.

2-7(4-x)=9

Someone please explain this backwards undoing stuff. I do NOT remember working problems this way in HS Algebra.

"UNDO"? I have never heard that used as a math term. :confused:

And I agree with momof7's method. :001_smile:

[mcconnellboys]

When I see "simplify", I think of removing all brackets or parentheses, so I would do this:

2-7(4-x)=9

2 - 28 +7x = 9
(Multiplying -7 x 4 and -7 times x in order to rid ourselves of the parentheses)

-26 + 7x = 9
Add 26 to each side

7x = 35
Divide by 7 on each side

x = 5

[Pam L in Mid Tenn]

Stacy:
Keep in mind that TT (and all programs really) teach ONE way to solve the problems. Some programs might give you two methods.

When my kids were in TT, and now in MUS, I would take the problem and solve it MY way and then check my answer. Most of the time MY was a correct method to a solution. Then, I would say something like... "MUS is teaching one method, here's how I would solve it. You can use whatever method gets the correct answer. Just let me see your work."

If you watch a few TT lessons yourself I think you can get a grasp on the unique words (like undoing) that they use.

Pam

[songbirdie]

Stacy:


If you watch a few TT lessons yourself I think you can get a grasp on the unique words (like undoing) that they use.

Pam

This is actually one of the two main shortcomings of TT, IMHO: they use terminology that your child will never see on any SAT, ACT, or other standardized test that they may need to get into college. It would be tragic if they got a low score because, even though they could maybe solve the problems, they wouldn't know what the test was asking because it uses standard math terminology and they never learned that.

[Teachin'Mine]

He may have gotten the wrong answer if he was distributing 7 instead of -7. The first solution in this thread is the "usual" way of solving this type of problem.

[EKS]

My son *hated* TT Geometry because he thought that the guy on the dvd sounded like he was talking to a group of preschoolers (and I had to agree). The ridiculous terms "simplify" and "undo", which I believe mean distribute and solve for x, respectively, are just part of the package. Apparently the authors of TT don't believe that students in high school can handle the vocabulary of math.