
Algebra PreAlgebra and Basic Algebra Math Forum 
 LinkBack  Thread Tools  Display Modes 
June 6th, 2014, 03:09 PM  #1 
Newbie Joined: Jun 2014 From: Caribbean Posts: 2 Thanks: 0  Could someone please explain these question?
I do not know how to do these but I tried. These are rational expressions. Please explain them, I want to learn how to do them. Thank you. 1. 1/x−1 + 4/x²−1 − 2/ x²−2x+1 my answer 1/x1 + 4/ (x1) (x+1)  2/ (x1) (x1) 2. 9 1/y²/ 3 1/y my answer: 6y 3. 5/t1 + 3/t my ans 8/ t(t1) 
June 6th, 2014, 04:06 PM  #2 
Math Team Joined: Dec 2013 From: Colombia Posts: 7,671 Thanks: 2651 Math Focus: Mainly analysis and algebra 
The aim is to merge all the terms in one quotient. We do this by finding a denominator that is the product of all the distinct elements in the denominators of the individual terms. The easiest way to do this is to simply multiply the denominators, but that is often more than you need to do and it can make the next part more complicated. Let's look at the first question. There are three denominators here, but your work in factorising then (a good first step) has shown that each contains $(x  1)$, so we'll need that in the combined denominator. Looking at the second term, we see an $(x + 1)$ in addition to the $(x  1)$, so we'll need that too. And the third denominator has a second $(x  1)$ term, so we'll include that too. Thus the denominator of our answer will be $(x  1)(x + 1)(x  1) = (x  1)^2(x + 1)$. Now we need to construct our numerator. Starting with the first term, we see in going from the original denominator $(x  1)$ to the combined denominator $(x 1)^2(x+1)$ we have multiplied by $(x1)(x+1)$. With any fraction, if we want it to retain the same value, we must multiply the top by the same value as we did the bottom. In this case, we get $(x  1)(x +1)$. This is the first term in our numerator. The denominator of the second term has been multiplied by $(x1)$, so we'll do the same to the numerator to get $4(x1)$. Finally, the third denominator was multiplied by $(x+1)$, so we do that to the numerator getting $2(x+1)$. Now we have scaled the numerators to preserve the value of the individual terms while giving them a common denominator. So we are ready to combine them, taking care to copy the operators from the original expression (in this case + then ). So $$\frac{1}{x1} + \frac{4}{(x1)(x+1)}  \frac{2}{(x1)(x+1)} = \frac{(x1)(x+1)}{(x1)^2(x+1)} + \frac{4(x1)}{(x1)^2(x+1)}  \frac{2(x+1)}{(x1)^2(x+1)} = \frac{(x1)(x+1) + 4(x1)  2(x+1)}{(x1)^2(x+1)}$$ Now we have a single expression as required. The numerator needs to be simplified, but that is all. You try the others again. Last edited by skipjack; June 7th, 2014 at 03:07 AM. 
June 6th, 2014, 08:21 PM  #3 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 14,597 Thanks: 1038 
They all boil down to this: a/b + c/d = (ad + bc) / (bd) 1/2 + 1/4 = 2/4 + 1/4 = (2+1) / 4 = 3/4 
June 7th, 2014, 04:47 PM  #4 
Newbie Joined: Jun 2014 From: Caribbean Posts: 2 Thanks: 0 
Than you. I have figure how to do these.


Tags 
explain, question 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
trying to explain simple infimum Question  lun123  Real Analysis  4  August 23rd, 2014 02:38 PM 
Help solve this word question and explain how you got it.  jasonxman  Algebra  3  December 8th, 2013 11:38 PM 
can someone solve and explain this question  yaasaay  Algebra  2  April 7th, 2011 02:11 PM 
i want to explain the solution to this question  rsoy  Algebra  6  December 8th, 2009 08:31 AM 
Kindly explain me first two question  moonnightingale  Calculus  0  September 16th, 2009 07:54 PM 