Equations with parenthesis?

misheeru · 2010-09-28 08:04:41

Hey guys, so we started doing some "simple" equations in math and I'm totally lost on some of these!

First off, I get the easier ones like:

5x + 2 = 12 (answer: x = 2)

or

6x - 8 = 16 (answer: x = 4)

But I'm having trouble solving for x in the more complicated ones like:

3(x + 2) = 16

7(2x + 6) = 1

or

4(3 - 2x) = 15

please help! I don't get these ones at all! Thanks!

bobbym · 2010-09-28 08:06:17

Hi;

3(x + 2) = 16

Expand them out first.

3x + 6 = 16

Now you know how!

misheeru · 2010-09-28 08:15:44

But since 3 doesn't go into 14 wouldn't out answer end up being a decimal?

bobbym · 2010-09-28 08:16:24

Where does th 14 come from?

misheeru · 2010-09-28 08:23:58

Like this?

3x + 2 = 16
- 2 -2

3x = 14

then I'm supposed to go on from there? Thats where 14 came from...

bobbym · 2010-09-28 08:25:45

Nope!

3(x + 2) = 16

3x + 6 not 3x + 2

misheeru · 2010-09-28 08:32:26

Oh, i missed that!

so then from there we go to...?

3x + 6 = 16
- 6 - 6

to 3x = 10?

am i good so far???

bobbym · 2010-09-28 08:34:30

Yes, when you multiply something that is in a parentheses you multiply everything.

3x = 10 is right but you have not solved for x.

misheeru · 2010-09-28 08:39:03

I know that. I was asking you if I had done it correctly so far.

Aren't we still going to end up with a decimal because 3 doesn't go into 10 evenly?

bobbym · 2010-09-28 08:41:45

Nope.

Rant:

I do not like the modern reptilian trend of eliminating fractions in place of decimals. This teaching startegy is so silly and from the standpoint of numerical analysis, funny.

End Rant:

You will end up with a beautiful fraction!!

misheeru · 2010-09-28 08:45:26

YUCK!

And you are going to be mad at me, when I tell you I just went back in my notes and checked and I copied the problem wrong to begin with.

bobbym · 2010-09-28 08:47:30

Nope, copying a problem is my biggest problem. I understand other people's mistakes because I make them all.

We will start with the new problem if you like.

misheeru · 2010-09-28 08:56:57

lol, okay thanks.

here is the real problem:

3(x + 2) = 6 (i really have no idea where i got 12 from)

okay so let me try this:

3(x + 2) = 6

3x + 6 = 6
- 6 - 6
3x = 0

x = 0

how does that look?

bobbym · 2010-09-28 08:58:28

That is correct. But too easy! Did your teacher provide that problem?

misheeru · 2010-09-28 09:18:35

No, its part of the assignment. Now that I know what I'm doing it is pretty easy.

What about this one:

5(x - 4) = 12

5x - 9 = 12
+9 +9

5x = 21

okay, so i can just tell we are going to end up with some crummy fraction... what do i do from here?

bobbym · 2010-09-28 09:29:50

Ho!

5(x - 4) = 12
5x - 9 = 12

Mind expanding 5(x-4) again. please.

misheeru · 2010-09-28 09:31:55

what do you mean?

5x - 9 = 12

that?

bobbym · 2010-09-28 09:34:00

5(x-4) ≠ 5x - 9

That up there is saying they do not equal each other. You must multiply everything in the parentheses, remember?

misheeru · 2010-09-28 09:36:02

opps i added instead of multiplying.

so its

5x - 20?

bobbym · 2010-09-28 09:38:17

Yes,

5x - 20 = 12 Now you should be an expert on what comes next.

misheeru · 2010-09-28 09:44:37

expert my.....

5x - 20 = 12
+20 +20

1/5 * 5x = 32 * 1/5

= 32/5?

Last edited by misheeru (2010-09-28 09:45:18)

bobbym · 2010-09-28 09:51:04

That's right, if you want to leave it as an improper fraction.

misheeru · 2010-09-28 09:52:29

yeah, it should be a mixed number right?

in forgot how to do that...uh isn't it something like you decide and the leftover becomes the bog number? Or something along those lines??

bobbym · 2010-09-28 10:00:28

Something like that. Want to see how?

misheeru · 2010-09-28 10:06:07

yes, please.

Math Is Fun Forum

#1 2010-09-28 08:04:41

Equations with parenthesis?

#2 2010-09-28 08:06:17

Re: Equations with parenthesis?

#3 2010-09-28 08:15:44

Re: Equations with parenthesis?

#4 2010-09-28 08:16:24

Re: Equations with parenthesis?

#5 2010-09-28 08:23:58

Re: Equations with parenthesis?

#6 2010-09-28 08:25:45

Re: Equations with parenthesis?

#7 2010-09-28 08:32:26

Re: Equations with parenthesis?

#8 2010-09-28 08:34:30

Re: Equations with parenthesis?

#9 2010-09-28 08:39:03

Re: Equations with parenthesis?

#10 2010-09-28 08:41:45

Re: Equations with parenthesis?

#11 2010-09-28 08:45:26

Re: Equations with parenthesis?

#12 2010-09-28 08:47:30

Re: Equations with parenthesis?

#13 2010-09-28 08:56:57

Re: Equations with parenthesis?

#14 2010-09-28 08:58:28

Re: Equations with parenthesis?

#15 2010-09-28 09:18:35

Re: Equations with parenthesis?

#16 2010-09-28 09:29:50

Re: Equations with parenthesis?

#17 2010-09-28 09:31:55

Re: Equations with parenthesis?

#18 2010-09-28 09:34:00

Re: Equations with parenthesis?

#19 2010-09-28 09:36:02

Re: Equations with parenthesis?

#20 2010-09-28 09:38:17

Re: Equations with parenthesis?

#21 2010-09-28 09:44:37

Re: Equations with parenthesis?

#22 2010-09-28 09:51:04

Re: Equations with parenthesis?

#23 2010-09-28 09:52:29

Re: Equations with parenthesis?

#24 2010-09-28 10:00:28

Re: Equations with parenthesis?

#25 2010-09-28 10:06:07

Re: Equations with parenthesis?

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