Add and Subtract Indicated

HellBunny · March 4th, 2012, 09:31 PM

$\frac{5}{2r+12} - \frac{1}{r}$ Okay, I know that I'm suppose to multiply the top and bottom so that the denominator is alike, but it's not. Ugh, I broke the bottom down to be $2(r+6)$ in the first column and this is where I'm lost, the "r" . . . I've tried making both denominatiors 2r(r+6) by multiplying 2(r+6)

just lost

The Chaz · March 4th, 2012, 09:39 PM

Quote:

Originally Posted by HellBunny

... I've tried making both denominators 2r(r+6) by multiplying [color=#000080]*** 1/r by ****[/color]2(r+6)

just lost

That's good.
You'll also need to multiply the first term by r/r

HellBunny · March 4th, 2012, 09:43 PM

It's still not coming out the right answer,

Denis · March 4th, 2012, 09:55 PM

What's the "right answer"? I get:

3(r - 4)
---------
2r(r+6)

??

HellBunny · March 4th, 2012, 09:57 PM

That's the answer. But what do you have on the second denominator when you're multiplying?

Denis · March 4th, 2012, 10:12 PM

Not sure what you're asking, HB, but here's my steps:

5 / (2r + 12) - 1 / r

= [5r - 1(2r + 12)] / [r(2r + 12)]

= (5r - 2r - 12) / (2r^2 + 12r)

= (3r - 12) / [2r(r + 6)]

= [3(r - 4)] / [2r(r + 6)]

Like:
a/b - c/d
= (ad - bc) / bd

Hope that helps instead of confuses

Being 7/10 bald-headed, I musy say I'm jealous of your Afro

HellBunny · March 5th, 2012, 12:25 AM

Thanks, I'll give you some hair.

March 4th, 2012, 09:31 PM	#1
HellBunny Member Joined: Feb 2012 Posts: 97 Thanks: 0	Add and Subtract Indicated $\frac{5}{2r+12} - \frac{1}{r}$ Okay, I know that I'm suppose to multiply the top and bottom so that the denominator is alike, but it's not. Ugh, I broke the bottom down to be $2(r+6)$ in the first column and this is where I'm lost, the "r" . . . I've tried making both denominatiors 2r(r+6) by multiplying 2(r+6) just lost
$HellBunny is offline$

March 4th, 2012, 09:43 PM	#3
HellBunny Member Joined: Feb 2012 Posts: 97 Thanks: 0	Re: Add and Subtract Indicated It's still not coming out the right answer,
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March 4th, 2012, 09:55 PM	#4
Denis Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,955 Thanks: 988	Re: Add and Subtract Indicated What's the "right answer"? I get: 3(r - 4) --------- 2r(r+6) ??
$Denis is online now$

March 4th, 2012, 09:57 PM	#5
HellBunny Member Joined: Feb 2012 Posts: 97 Thanks: 0	Re: Add and Subtract Indicated That's the answer. But what do you have on the second denominator when you're multiplying?
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March 4th, 2012, 10:12 PM	#6
Denis Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,955 Thanks: 988	Re: Add and Subtract Indicated Not sure what you're asking, HB, but here's my steps: 5 / (2r + 12) - 1 / r = [5r - 1(2r + 12)] / [r(2r + 12)] = (5r - 2r - 12) / (2r^2 + 12r) = (3r - 12) / [2r(r + 6)] = [3(r - 4)] / [2r(r + 6)] Like: a/b - c/d = (ad - bc) / bd Hope that helps instead of confuses Being 7/10 bald-headed, I musy say I'm jealous of your Afro
$Denis is online now$

March 5th, 2012, 12:25 AM	#7
HellBunny Member Joined: Feb 2012 Posts: 97 Thanks: 0	Re: Add and Subtract Indicated Thanks, I'll give you some hair.
$HellBunny is offline$

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