# How do you add Rational Expressions when youre in University Math?

## Main Question or Discussion Point

Cross multiply ...
and then multiply by the common denominator...

how do you do it

or the other way

It seems like cross multiplying is less formal ...and I dont know if its 'right' to take the shortcut --since you have to do this so much

If you have more than two like with a partial fractions problem ...im obviously going to just mult/divide by the common denominator

But how do you do it in general ...

symbolipoint
Homework Helper
Gold Member
Which kind of institution makes no difference. You use the same properties and axioms with rational expressions addition no matter whether you are in college, community college, or university. Adding rational expressions? Use lowest common denominator and raise either or both rational expressions to higher terms. This is the same idea whether you have rational fractions, complex fractions, rational expressions(using variable).

symbolipoint
Homework Helper
Gold Member
.... in other words, what you learned in Algebra 1 and Algebra 2 still works.

$$\frac{a}{b} + \frac{c}{d}=\frac{da + bc}{bd}$$

No...I no how to do it

im just wondering how you do it persoally

symbolipoint
Homework Helper