simplifying rational expressions: 7/(3x + 9) + 4/(4x + 12)

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rls4973

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Oct 30, 2008
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17
7 4
---- + -----
3x+9 4x+12

equals

11
----------
7x+21

???? or am i way off? Thanks in advance :)
 
Re: just checking



You responded to my previous post, so I had thought that you read it.

Since you do not make an effort to preview your posts, I do not make an effort to decipher them.

 
rls4973 said:
7 4
---- + -----
3x+9 4x+12
Click to expand...
The poster appears to mean the following:

. . . . .[ 7 / (3x + 9) ] + [ 4 / (4x + 12) ]
 
rls4973 said:
7 4
---- + -----
3x+9 4x+12

equals

11
----------
7x+21

???? or am i way off? Thanks in advance :)
Click to expand...

You are way off!!

What is:

\(\displaystyle \frac{1}{2} \, + \, \frac{1}{2} \, = \, ???\)

certainly not (1+1)/(2+2).

How would you calculate (without calculator)

\(\displaystyle \frac{3}{5} \, + \, \frac{2}{3} \, = \, ???\)

Follow the exact same procedure..
 
at first i did factor out the bottom to be 3(x+3)and 4(x=3) but than I wanted to flip so i could cross cancel but i dont think you can do that over a plus sign... so I need to get a common denomenator right
 
rls4973 said:
at first i did factor out the bottom to be 3(x+3)and 4(x=3) but than I wanted to flip so i could cross cancel but i dont think you can do that over a plus sign... so I need to get a common denomenator right ... yes -- then what?
Click to expand...

Before doing anything else, please show me - how would you calculate (as a fraction - without a calculator) -

\(\displaystyle \frac{3}{5} \, + \, \frac{2}{3} = ??\)
 
rls4973 said:
i would get a common denom like 15
Click to expand...

Correct and complete the addition for me - showing the steps (for the numerical example)
 
rls4973 said:
3*3 2*5
------------
15
Click to expand...
I will guess that you forgot the "plus" sign, neglected to show some of your steps, and that you actually meant us to figure out the following:

. . . . .3/5 + 2/3

. . . . .(3/5)(3/3) + (2/3)(5/5)

. . . . .(3*3)/(5*3) + (2*5)/(3*5)

. . . . .9/15 + 10/15

. . . . .(9 + 10)/15

. . . . .19/15

I could be wrong, of course. It appears that you have still not read the formatting articles whose links you saw when you read the "Read Before Posting" thread. Please go read one or both of those articles now, so that your future posts will be understandable.

Thank you.

Eliz.
 
rls4973 said:
3*3 2*5
------------
15

which equals

19
----
15
Click to expand...

You are skipping steps:

\(\displaystyle \frac{3}{5} \, + \, \frac{2}{3}\)

Your LCD is

\(\displaystyle 5\cdot 3 \, = \, 15\)

\(\displaystyle = \, \frac{3}{5} \cdot \frac{3}{3}\, + \, \frac{2}{3}\cdot \frac{5}{5}\) ... This is a very important step for "algebraic expressions"

\(\displaystyle = \, \frac{9}{15} \, + \, \frac{10}{15}\)

\(\displaystyle = \, \frac{(9 \, + \, 10)}{15}\)

\(\displaystyle = \, \frac{19}{15}\)

Now follow the exact same steps for your algebraic expressions.
 
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