# Adding and Subtracting using LCD

#### Katie1

##### New member
I am having problems doing this, I can do the simple ones such as[3/4b^2+5/3b^3
But when I get to 2x/(x^2+5x+6)-4/(x-2) I get lost.
LCD for (x^2+5x+6)=(x-2)(x-3)
LCD for (x-2)= (x-2)
So the LCD= (x-2)(x-3)?

#### Subhotosh Khan

##### Super Moderator
Staff member
Katie1 said:
I am having problems doing this, I can do the simple ones such as[3/4b^2+5/3b^3
But when I get to 2x/(x^2+5x+6)-4/(x-2) I get lost.
LCD for (x^2+5x+6)=(x-2)(x-3)
LCD for (x-2)= (x-2)
So the LCD= (x-2)(x-3)-----------Yes?
Say you want find LCD of 3 and 15

3 = 3

15 = 3 * 5

LCD(3,5) = 3*5 = 15

Say you want find LCD of 9 and 15

9 = 3 * 3

15 = 3 * 5

LCD(3,5) = 3*3 *5 = 45

#### Loren

##### Senior Member
LCD for (x^2+5x+6)=(x-2)(x-3)
LCD for (x-2)= (x-2)
So the LCD= (x-2)(x-3)-----------Yes?

NO!

Your factorization of x^2+5x+6 is not correct.

#### Katie1

##### New member
It would have been if I had typed the problem correct. Here is what i have..
LCD(x-2)(x-3)

2x/(x-2)(x-3)+(4(x-3)/(x-2)(x-3)
(2x+4x-12)/(x-2)(x-3)
(6x-12)/(x-2)(x-3)
6(x-2)/(x-2)(x-3)
6/(x-3)