combining like terms in a linear equation.  TOPIC_SOLVED

Simple patterns, variables, the order of operations, simplification, evaluation, linear equations and graphs, etc.

combining like terms in a linear equation.

Postby kimkiunke on Fri Feb 15, 2013 7:28 pm

I can't seem to finish this problem. I'm fine until the combining like terms on each side. Is there a set of rules like if one of the terms is on the opposite side of the = then you subtract?? There doesn't seem to be a pattern to follow to get the right answer:

-7(y+1) =4y-6+2(2y+4)
-7y-7+4y-6+4y+8
-7y-7=8y+2
-7y=8y+9

I get all of this so far. Here is where I have trouble. Is there a set pattern to this? Because I never seem to get the write answer using the same formula:
-15y=9 I guess it's -7y+8Y and you get -15? How is that? If I add -7+8 I get 1 not -15. It looks like it's just 7+8 but how does it stay negative and how do I know that when solving? Example, what if it was 7y= -8Y? Would it still be -15? SO frustrating! I get everything but this part. :confused:
kimkiunke
 
Posts: 1
Joined: Fri Feb 15, 2013 7:09 pm

Sponsor

Sponsor
 

Re: combining like terms in a linear equation.  TOPIC_SOLVED

Postby jg.allinsymbols on Fri Feb 15, 2013 8:04 pm

kimkiunke wrote:I can't seem to finish this problem. I'm fine until the combining like terms on each side. Is there a set of rules like if one of the terms is on the opposite side of the = then you subtract?? There doesn't seem to be a pattern to follow to get the right answer:

-7(y+1) =4y-6+2(2y+4)
-7y-7+4y-6+4y+8
-7y-7=8y+2
-7y=8y+9

I get all of this so far. Here is where I have trouble. Is there a set pattern to this? Because I never seem to get the write answer using the same formula:
-15y=9 I guess it's -7y+8Y and you get -15? How is that? If I add -7+8 I get 1 not -15. It looks like it's just 7+8 but how does it stay negative and how do I know that when solving? Example, what if it was 7y= -8Y? Would it still be -15? SO frustrating! I get everything but this part. :confused:


Sure, the rule is properties of equality. You do the same thing to both sides of the equation. What is stopping you from adding the additive inverse of 8y to both sides? Then you have something to combine.
jg.allinsymbols
 
Posts: 71
Joined: Sat Dec 29, 2012 2:42 am

Re: combining like terms in a linear equation.

Postby maggiemagnet on Wed Feb 27, 2013 1:54 pm

Comment: Thank you for showing your steps and thinking so clearly! :thumb:

kimkiunke wrote:-7y=8y+9

I get all of this so far. Here is where I have trouble....
-15y=9 I guess it's -7y+8Y and you get -15?

Not quite. You have to subtract the 8y from both sides to move it from the right to the left. You can see worked examples here.
:clap:
User avatar
maggiemagnet
 
Posts: 298
Joined: Mon Dec 08, 2008 12:32 am


Return to Pre-Algebra