# Thread: Explanation - Process of finding an LCD

1. ## Explanation - Process of finding an LCD

1. Explain the process of finding the least common denominator (LCD) - make sure your explanation works for ALL possible rational expressions.

2. What happens if you get a common denominator, but not the LEAST common denominator?
Can anyone post a step by step process?

2. Originally Posted by chrozer
Can anyone post a step by step process?
the "rational" expressions we are talking about here. are they just integers? because then, we find the LCD by finding the LCM (least common multiple) of all the denominators of the terms. (I suppose you know how to do this?)

if it is not the LCD, then we will be able to factor out something in the numerator that cancels with the common denominator you found, leaving us with the LCD. hope that helps

3. Originally Posted by Jhevon
the "rational" expressions we are talking about here. are they just integers? because then, we find the LCD by finding the LCM (least common multiple) of all the denominators of the terms. (I suppose you know how to do this?)

if it is not the LCD, then we will be able to factor out something in the numerator that cancels with the common denominator you found, leaving us with the LCD. hope that helps
I think when it means "rational expressions" it means like finding an LCD for $\frac {x^2+4}{x^2-4} + \frac {x^2-4}{x^2+4}$

4. Originally Posted by chrozer
I think when it means "rational expressions" it means like finding an LCD for $\frac {x^2+4}{x^2-4} + \frac {x^2-4}{x^2+4}$
This works in general. $\frac ab \pm \frac cd = \frac {ad \pm bc}{bd}$

if bd is not the LCD, then we will be able to factor something out from $ad \pm bc$ to cancel the extra factors in bd