# Interactive video lesson plan for: Multiplying functions - How to find the product of functions

#### Activity overview:

► My Algebra 1 course: https://www.kristakingmath.com/algebra-1-course

In this video we're talking about how to find the product of two functions. In other words, if we want to multiply two functions together, how do we do it and what will we get when we do?

0:12 // What is the "product of functions"?
0:23 // How to do you write the product of two functions?
1:01 // Multiplying functions that are numbers (constants)
1:31 // Multiplying functions that have variables
2:35 // Finding fg(2): the value of the product function at x=2

When you have multiple functions, you can use some simple rules to find their sum, difference, product, or quotient. In this video we're going to focus on how to find the product of two functions.

As you might guess, finding the product of functions is as simple multiplying the functions together. When you multiply two functions together, you'll get a third function as the result, and that third function will be the product of the two original functions.

For example, if you multiply f(x) and g(x), their product will be h(x)=fg(x), or h(x)=f(x)g(x). You can also evaluate the product at a particular point. So if you want to know the value of the product at x=2, you can plug x=2 into the product function h(x) to find h(2)=fg(2)=f(2)g(2).

Alternately, instead of first finding the product function, and then evaluating at x=2, you could first evaluate both f(x) and g(x) at x=2, and then multiply those results together to get the product h(2).

Music by Joakim Karud: http://soundcloud.com/joakimkarud

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Hi, I’m Krista! I make math courses to keep you from banging your head against the wall. ;)

Math class was always so frustrating for me. I’d go to a class, spend hours on homework, and three days later have an “Ah-ha!” moment about how the problems worked that could have slashed my homework time in half. I’d think, “WHY didn’t my teacher just tell me this in the first place?!”

So I started tutoring to keep other people out of the same aggravating, time-sucking cycle. Since then, I’ve recorded tons of videos and written out cheat-sheet style notes and formula sheets to help every math student—from basic middle school classes to advanced college calculus—figure out what’s going on, understand the important concepts, and pass their classes, once and for all. Interested in getting help? Learn more here: http://www.kristakingmath.com

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