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## Get ready for Algebra 2

### Course: Get ready for Algebra 2>Unit 3

Lesson 1: Evaluating functions

# Worked example: Evaluating functions from equation

Learn how to evaluate f(x)=49-x² at x=5. Created by Sal Khan.

## Want to join the conversation?

• Can anybody help me find the output, k, when the input, t, is −7.
k = 10t-19
k = ?

I need a hand. Thank you
• You just neet to replace "t" with the given value "-7"
k = 10(-7)-19
Then, follow order of operations rules to calculate the value of "k".
Give it a try. Comment back if you get stuck or have questions.
• 1. Can a function have name like add(x) instead of f(x)?
2. Can a function have more than 1 argument, like f(a, b, c)?
3. Can a function's argument have a name like "apes", "apples" instead of "x", "y"?
• 1. Yes. In mathematics it is more common to use a single letter (sometimes a Greek letter), but a function name can be anything. After all it's just a way to communicate to other humans what you're talking about, changing a name doesn't change the math.
2. Yes. A simple example is f(x,y) = x * y.
3. Yes. See answer 1: single letter names are conventional, but not required. They're all just names. You could even draw pictures instead of using letters - in fact, Khan Academy does that in some early math videos.
• does anyone know how to do this?
• Can Someone Help Me Solve This Function?
f(0)^2
where f(x)=3x+4
• Find f(0): f(0) = 3(0) + 4
Once you know, f(0), square the result.
• How do you know where the output is?
• What are the general rules for solving functions?
• like terms should ALWAYS be combined, that's one thing you can keep in mind
• So the "f" in f(x) stands for function? As in solve the function with whatever the x variable may be?
• That's not quite right, it's more accurate to say that "f" is the name of the function. You can name a function whatever you want, but f is just the most common one people use.
You're right otherwise. If you see f(5), you just evaluate with x=5.
• how will you make a mathematical model for this:
You and your classmates want to earn extra income this summer. To do
this, you will sell Fun Shirts. The wholesaler has the following
conditions: If you purchase 100 shirts, each shirt costs P120; if you
purchase between 200 to 300 shirts, the price per shirt is lowered to
P110; if you get more than 300 shirts, the price per shirt is lowered by 15. thank you.