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

PhysicsHelp12
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 don't 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 ...

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).

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

epkid08
$$\frac{a}{b} + \frac{c}{d}=\frac{da + bc}{bd}$$

PhysicsHelp12
No...I no how to do it

im just wondering how you do it persoally

Homework Helper
Gold Member
No...I no how to do it

im just wondering how you do it persoally

The post #4 has it correctly. If the rational expressions are composed of few enough characters, then some of us may do one of the steps in our heads, but doing steps in our heads is not a requirement. One can often use a scientific calculator efficiently after writing the rational expression before or after any simplification step. One does what one is comfortable doing as long as the correct axioms and properties are used.