Solving Equations using two properties

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Please I need help with this equation.No matter how I do it, the answer is wrong. 12-3x=7x-4. I know the answer is 8/5 but how do I get that?
 
Can you show at least one way that you tried to solve the problem?
 
Bonnie said:
Please I need help with this equation.No matter how I do it, the answer is wrong. 12-3x=7x-4. I know the answer is 8/5 but how do I get that?
Ok so you have 12-3x=7x-4
1)So you switch the 12 and 7x so that it reads: -3x-7x=-12-4

2) then you work out the answer to -3x-7x which would be -10

3) work out the other side (-12-4) which will be -16

4) you should now have -10x=-16

5) move the 10 over the = sign so it reads x=16/10 (the negatives are cancelled out)

6)divide and your answer will be 8/5

I hope this helps... :)

~ainsley~ :twisted:
 
happy said:
Can you show at least one way that you tried to solve the problem?
Yes. 12-3x=7x-4
12-3x+3=7x-4+3
12+3=7x-4+3
15=3+3
15=6
 
Ainsley said:
1)So you switch the 12 and 7x
2) then you work out the answer to -3x-7x which would be -10
5) move the 10 over the = sign
I dare you to show me in a text book where these operations are defined:

"Switch"
"Work Out"
"Move Over the Equal Sign"

Are you studying on your own? You may still be learning something useful, but if someone is getting paid to show you how to do this, someone needs to be slapped.

You should be studying/learning/memorizing properties, laws, theorems, and reliable procedures.
 
It is in the basic college mathematics book 5th edition by John Tobey and Jeffery Slater
 
Bonnie, it is my sincere hope that you mean the information you are SUPPOSED to be learning is in that book, NOT the foolishness to which I was referring.

Let's see what you are doing.

12-3x=7x-4
12-3x+3=7x-4+3

You went astray right off. Why did you add '3' to each side? You've no '3' in there. Add '4' to each side or add '3x' to each side.


12 - 3x = 7x - 4

Add '4' to each side.

12 - 3x + 4 = 7x - 4 + 4

Commutative Property of Addition

12 + 4 - 3x = 7x - 4 + 4

Associative Property of Addition

(12 + 4) - 3x = 7x - 4 + 4

Distributive Property of Multiplication over Addition

(12 + 4) - 3x = 7x - (4 - 4)

Addition/Substitution

16 - 3x = 7x - (4 - 4)

Additive Inverse Property

16 - 3x = 7x - 0

Additive Property of Zero

16 - 3x = 7x

These rules and properties (and an occasional convention) allow us to proceed consistently and deliberately.

Now what?
 
This is an example out of the book of what I have to learn;
-5+2y+8=7y+23
2y+3=7y+23
2y+(-7y)+3=7y+(-7y)+23
-5y+3=23
-5y+3+(-3)=23+(-3)
-5y=20

-5y/-5=20/-5
y=4

I just do not understand it.
 
Tk already told you what you were doing wrong. You can't pull numbers out of "thin air" and add them to your problem. Also, your adition and subtraction skills are kind of off the mark and you lost the variable. You can't end with "15=6".
 
Bonnie, It is so simple. There is the essence “whatever one does to one side of an equation one MUST so to the other side."
Look at your equation: 12-3x=7x-4
Add 3x to both sides: 12=10x-4, (because –3x+3x=0 & 12+0=12)
Add 4 to both sides of the new equation: 16=10x.
Divide both sides by 10: 16/10 = x (because 10x/10 = x).
 
pka said:
whatever one does to one side of an equation one MUST so to the other side."
See, one of those important principles I was talking about. There are others, some of which are listed in my longest post, above.
 
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