
Algebra PreAlgebra and Basic Algebra Math Forum 
 LinkBack  Thread Tools  Display Modes 
October 18th, 2008, 02:52 PM  #1 
Newbie Joined: Aug 2008 Posts: 16 Thanks: 0  Using LCD to Add and Subtract Rational Expressions
My math book has a guide on how to add and subtract two rational expressions with different denominators. The question is: I know the LCD's are and the book then says to multiply the numerator and denominator of by WHY do I multiply the numerator by instead of if is supposed to be the LCD? so both expressions end up looking like: Thanks! 
October 18th, 2008, 11:58 PM  #2 
Global Moderator Joined: Dec 2006 Posts: 20,267 Thanks: 1958  The LCM of the denominators is To change the denominator of each fraction to the LCM, you have to multiply the numerator and denominator of the first fraction by and of the second fraction by Can you see why now? 
October 19th, 2008, 02:33 PM  #3 
Newbie Joined: Aug 2008 Posts: 16 Thanks: 0  Re: Using LCD to Add and Subtract Rational Expressions
I see. So you don't have to multiply by the LCD to GET the denominators to be the same. And the factors you used to get them to be the same equal also be used in the numerators, correct? Thanks! 
October 19th, 2008, 04:33 PM  #4 
Global Moderator Joined: Dec 2006 Posts: 20,267 Thanks: 1958 
Correct. I hope you can see how the factors are obtained.

October 20th, 2008, 08:00 AM  #5  
Senior Member Joined: Jul 2008 Posts: 895 Thanks: 0  Re: Using LCD to Add and Subtract Rational Expressions Quote:
 

Tags 
add, expressions, lcd, rational, subtract 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Rational expressions help.  link107  Algebra  3  February 26th, 2012 08:08 PM 
Rational expressions help.  link107  Algebra  4  February 25th, 2012 10:33 PM 
rational expressions  boomer029  Algebra  3  January 10th, 2012 08:11 AM 
Rational Expressions  symmetry  Algebra  3  June 25th, 2007 12:53 PM 
LCD of Rational Expressions  symmetry  Algebra  1  June 25th, 2007 05:56 AM 