# Dividing Rational expressions

• Nov 16th 2007, 09:37 PM
t-dot
Dividing Rational expressions
i don't think that the answer in the book is right for this one

$\displaystyle \frac{15a^2b}{4c} \div \frac{8abc}{-3}$

i know that you have to times it by the reciprocal
the non-reduced answer that i got is:

$\displaystyle -\frac{45a^2b}{60a^2bc}$

the only way that i can think to reduce this is by dividing the top and bottom by 5 but that leaves 9 on the top and 12 on the bottom which can be reduced further.
also
the answer in the back of the book is

$\displaystyle -\frac{45a}{32c^2}$
how do you get it if it is.
• Nov 17th 2007, 04:04 AM
earboth
Quote:

Originally Posted by t-dot
i don't think that the answer in the book is right for this one

$\displaystyle \frac{15a^2b}{4c} \div \frac{8abc}{-3}$

i know that you have to times it by the reciprocal
the non-reduced answer that i got is:

$\displaystyle -\frac{45a^2b}{60a^2bc}$

the only way that i can think to reduce this is by dividing the top and bottom by 5 but that leaves 9 on the top and 12 on the bottom which can be reduced further.
also
the answer in the back of the book is

$\displaystyle -\frac{45a}{32c^2}$
$\displaystyle \frac{15a^2b}{4c} \div \frac{8abc}{-3}= \frac{15a^2b}{4c} \cdot \frac{-3}{8abc}$
As you easily can see you calculated $\displaystyle 4 \cdot 8 = 60$ which isn't correct too often :D