• Support PF! Buy your school textbooks, materials and every day products Here!

Need help with this algebra Q.

  • Thread starter tehmatriks
  • Start date
  • #1
40
0
Question is:
Evaluate 2/x+2 + 3/2x+1 when x= ½

back of the book says 2 and three tens i.e 2 3/10
 

Answers and Replies

  • #2
360
0
Throw some parentheses in there:

2/(x+2) + 3/(2x+1)

and you should get the answer in the back of the book.
 
  • #3
40
0
i know, i checked the back of the book and it says the answer is 2 3/10

this is how im doing it:
2/x+2 + 3/2x+1
=> 2/½+2 + 3/2(½)+1
=> 2/2½ + 3/2, get LCM of 2½ and 2, which is 10
=> 10(2)/2½ + 10(3)/2
=> 4(2) + 5(3)
=> 8 + 15 = 23

and i did it another way where i got 1 1/9
but i can't seem to get 2 3/10
 
  • #4
33,513
5,195
i know, i checked the back of the book and it says the answer is 2 3/10
Did you not understand spamiam's comment about parentheses? You seem to have glossed right over it.
this is how im doing it:
2/x+2 + 3/2x+1
=> 2/½+2 + 3/2(½)+1
=> 2/2½ + 3/2, get LCM of 2½ and 2, which is 10
=> 10(2)/2½ + 10(3)/2
=> 4(2) + 5(3)
=> 8 + 15 = 23
1.Use parentheses when a numerator or denominator (or both) have two or more terms.
2. Do not use => (implies) when you mean = (equals).

If x = 1/2, then 2/(x + 2) + 3/(2x + 1) = 2/(5/2) + 3/2 = 2 * 2/5 + 3/2 = 4/5 + 3/2

Now, the LCM of 5 and 2 is 10, so multiply the first fraction by 2/2 and the second by 5/5. After you do this, you will be able to combine the two fractions.

The answer in the book is correct.

and i did it another way where i got 1 1/9
but i can't seem to get 2 3/10
 
  • #5
40
0
Did you not understand spamiam's comment about parentheses? You seem to have glossed right over it.
nah, i didn't, i had no idea you had to put it in parentheses when you had more than one term in either the numerator or the denominator.

1.Use parentheses when a numerator or denominator (or both) have two or more terms.
2. Do not use => (implies) when you mean = (equals).

If x = 1/2, then 2/(x + 2) + 3/(2x + 1) = 2/(5/2) + 3/2 = 2 * 2/5 + 3/2 = 4/5 + 3/2

Now, the LCM of 5 and 2 is 10, so multiply the first fraction by 2/2 and the second by 5/5. After you do this, you will be able to combine the two fractions.

The answer in the book is correct.
nice job, thanks
only bit i dont understand is why and how 2/(½+1) became 2/(5/2)

and i apologize for my idiocy thus far :smile:

no wait, scratch that, i dont understand anything, forget i asked
 
Last edited:
  • #6
33,513
5,195
nah, i didn't, i had no idea you had to put it in parentheses when you had more than one term in either the numerator or the denominator.
The problem is that when you write 2/x + 2 + 3/2x + 1, knowledgeable people will probably interpret this as
[tex]\frac{2}{x} + 2 + \frac{3}{2x} + 1[/tex]

or even as
[tex]\frac{2}{x} + 2 + \frac{3}{2}x + 1[/tex]


which is not at all what you intended.
nice job, thanks
You're welcome!
only bit i dont understand is why and how 2/(½+1) became 2/(5/2)
It didn't, but 2/(1/2 + 2) = 2/(5/2)
and i apologize for my idiocy thus far :smile:
The goal is to get you to learn from your mistakes.
 
  • #7
40
0
ok im back, thanks for the help mark, i realised what i was doing wrong, i took it too far, i got the answer pretty much right at the beggining, except it all went downhill when i used the LCM

anyway, preciate the help fellas, i've been trying to figure this out for 6+ hrs and was getting alittle depressed, happy now tho, peace
 

Related Threads on Need help with this algebra Q.

  • Last Post
Replies
1
Views
908
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
1
Views
835
  • Last Post
Replies
5
Views
726
  • Last Post
Replies
1
Views
3K
  • Last Post
Replies
1
Views
960
  • Last Post
Replies
14
Views
3K
  • Last Post
Replies
6
Views
3K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
15
Views
6K
Top