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Algebra help? - October 18th 2015, 11:21 PM

When solving an equation such as 7-5x=-43, how would you handle the subtraction? From what I gather, because the subtraction is before the multiplication, you treat it differently than if it were 5x-7=-43. Is this true, and if so, what is the rule?


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Re: Algebra help? - October 18th 2015, 11:40 PM

I was taught to start by reading the sign immediately in front of the number, so the left side isn't subtraction, you're dealing with negative numbers. If it helps you can rearrange it as -5x+7= -43 then solve it. Just be careful not to lose the signs or your answer ends up wrong..


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Re: Algebra help? - October 19th 2015, 01:32 AM

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Originally Posted by Kate* View Post
I was taught to start by reading the sign immediately in front of the number, so the left side isn't subtraction, you're dealing with negative numbers. If it helps you can rearrange it as -5x+7= -43 then solve it. Just be careful not to lose the signs or your answer ends up wrong..
I'm pretty sure that I get it now. So if it were 7+5x=-43, would I change it to 5x+7=-43?


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Re: Algebra help? - October 19th 2015, 03:10 AM

I think your answer has the wrong sign that way.

All of the values need to keep their signs, otherwise the answer is wrong so it can change from

7-5x=-43 to either +7-5x=-43 or -5x+7=-43


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Re: Algebra help? - October 19th 2015, 03:53 AM

It's a negative number. So you would divide the whole equation by - 5.


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Re: Algebra help? - October 19th 2015, 05:03 AM

I'm going to try to explain this the best that I can and hope it makes a little bit of sense.

Kate is definitely right about making sure the sign stays with the number. The - is part of the 5x, so it needs to stay attached to it, regardless of the order you write the equation in.

To solve this particular equation, you want to subtract 7 from both sides. The reason for this is that you want to have your unknown variables (x) on one side and your real numbers on the other. When you subtract 7 from each side, you will be left with -5x=-50.

From there, you want to divide each side by -5 to get the x by itself. So, you would do the following: -5x/-5=-50/-5. Your answer would be 10.

I hope this made sense to you. If you need me to clarify any part of it, feel free to shoot me a message and I'll be happy to see what I can do.


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Re: Algebra help? - October 19th 2015, 10:22 PM

I was taught that whenever you move a number from one side to another, it changes to an opposite sign e.g. plus to minus and vice versa and multiplication becomes divide and vice versa. So I would work it out as:

7-5x=-43
-5x=-43-7 (plus 7 changes to minus 7)
-5x=-50
x=-50/5 (minus 5 becomes plus five, multiplication becomes divide)
x=-10

Hope that helps (or at least not confuse you!)


Edit: kate is right. Sorry, I must have been thinking of another equation with that method


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Re: Algebra help? - October 19th 2015, 11:22 PM

Quote:
Originally Posted by DutchWelshWolf View Post
I was taught that whenever you move a number from one side to another, it changes to an opposite sign e.g. plus to minus and vice versa and multiplication becomes divide and vice versa. So I would work it out as:

7-5x=-43
-5x=-43-7 (plus 7 changes to minus 7)
-5x=-50
x=-50/5 (minus 5 becomes plus five, multiplication becomes divide)
x=-10

Hope that helps (or at least not confuse you!)


This works too, but The 5 doesn't change sign because it doesn't change sides, so you divide by -5, not 5 and the answer is 10 not -10


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