# Week 14 -Rational Expressions and Equations

This week we learned how to make a function simply

For example:

$\frac{x^2-9}{x^2+8x+15}$

we need to factor first

so $\frac{(x+3)(x-3)}{(x+3)(x+5)}$

we can see the same thing from the top and the bottom, so we can get rid of them

so it is (x+3)

After that we can get $\frac{(x-3)}{(x+5)}$

Next step we have to make sure the range of values of “x” and what number can’t it become,

First we can see this formula:$\frac{(x+3)(x-3)}{(x+3)(x+5)}$ for values of bottom can’t be “0”

“x “can’t be -3 and -5

second we can see this formula :$\frac{(x-3)}{(x+5)}$ ,in the bottom x can’t be  -5

WARNING : you have to check the all function , even the first one ,one special is start by diving by a fraction , and then you have to multiply by the inverse of that fraction , and you have to look at the denominator of that fraction to make sure that the unknow numbers  before and after reciprocal and which number can’t be.(“0″ CAN’T BE THE BOTTOM”)