# Week 15

This past week in Pre Calculus 11 we finished Chapter 7: Rational Expressions and Equations. Something I learned this week was how and when to cross multiply. The rules when cross multiplying are it has to be two fractions with an equal sign between them. Here is an example:

$\frac{3}{q-2}=\frac{5}{q+4}$

Multiply 3(q+4) and 5(q-2)

= 3q+12=5q-10

Isolate q: 11=q

An example of what an equation that would not be able to cross multiply is $\frac{3}{4}\cdot\frac{2}{3}=\frac{6}{5}$ because it has 3 fractions and not 2.