1. ## fractions common demoninator

whats the LCD for

b 2b
-- --
(b+5) (b-5)

and

1 3
-- --
2xy x^2

and

1 5
-- --
12a^2b 18b^2

and

6 4x
-- --
x-3 (x-3)^2

there all two fractions by the way i have no idea what the sign is for fractions on the internet

2. Originally Posted by elfen_lied
whats the LCD for

b 2b
-- --
(b+5) (b-5)

and

1 3
-- --
2xy x^2

and

1 5
-- --
12a^2b 18b^2

and

6 4x
-- --
x-3 (x-3)^2

there all two fractions by the way i have no idea what the sign is for fractions on the internet
Hello,

you asked for the LCD only: If you can't factor the denominators the LCD is the product of both denominators:

$\displaystyle \frac{b}{b+5},\ \frac{2b}{b-5}\ \underbrace{\longrightarrow}_{denominator} (b+5)(b-5)=b^2-25$

$\displaystyle \frac{1}{2xy},\ \frac{3}{x^2}\ \underbrace{\longrightarrow}_{denominator}2x^2y$

$\displaystyle \frac{1}{12a^2 b},\ \frac{5}{18 b^2}\ \underbrace{\longrightarrow}_{denominator}36a^2 b^2$

$\displaystyle \frac{6}{x-3},\ \frac{4x}{(x-3)^2}\ \underbrace{\longrightarrow}_{denominator} (x-3)^2$

EB