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See how to create the four functions in this practice session.

#### Resources

- Understanding the Order of Operations:
**PEMDAS (Please Excuse My Dear Aunt Sally)**

How did it go? 0:00 If you didn't get it to work, you can watch my solution, 0:01 compare it to what you wrote, and then try to recreate it yourself. 0:04 Also, keep in mind there are often different ways to solve 0:07 a programming challenge. 0:10 Your solution may be different than mine and still work, that's fine. 0:11 Okay, first I'll use the script tag to attach this JavaScript file 0:15 to the index.html file. 0:19 Because the geometry.js file is inside a JavaScript folder, 0:23 js, the complete path from the index to the JavaScript file is js/geometry.js. 0:28 Okay, next I'll create a function. 0:35 I use the function keyword followed by the name of the function, 0:39 a pair of parentheses, and then some braces. 0:43 I'll name this areaRectangle. 0:47 You probably used a different name, and that's fine. 0:49 As long as the name clearly indicates what the function does, you're doing well. 0:51 Okay, this function needs two parameters to capture the width and 0:55 height values that are passed to it when the function's called. 0:59 Parameters go inside the parentheses. 1:02 And the programming for the function goes inside the braces. 1:11 The area is just the width times the height, so I'll use a simple return 1:15 statement, That returns the result of this calculation. 1:19 Calculating the volume of a box is pretty much the same. 1:26 It just requires a third parameter, the length. 1:30 Now, calculating the area of a circle requires a bit more JavaScript. 1:36 But I'll start with the basic function structure first. 1:41 This function will only take one argument, the radius of the circle. 1:44 Now, to calculate the area of the circle, 1:49 we need to do some more complex math using the value of pi. 1:52 Fortunately, the JavaScript math object includes the value of pi built into it. 1:56 Math.PI, then to calculate the area, we multiple this by the square of the radius. 2:00 To calculate the square of a value, you can use the Math.pow method. 2:08 Pow stands for power, and it lets you raise the value to a given power. 2:14 In this case, I want to square the radius or 2:18 raise the radius value to the second power. 2:21 The pow method takes the value that you wish to raise, 2:24 here it's the radius, and the value that you wanna raise it to. 2:27 In this case, I wanna square the radius, so I use 2 for this value. 2:31 Now, calculating the volume of a sphere is similar. 2:35 You need to use pi and you also need to use pow. 2:38 But this time you'll raise it to the third power. 2:40 Notice that I wrapped the 4 divided 3 inside parentheses. 2:44 This helps group that mathematical statement and 2:48 makes it clear to me that I'm looking at four-thirds here, or 4 divided by 3. 2:50 Now, this is related to the order of operations, 2:55 something you may remember from a math class. 2:57 I've added a link to the teacher's notes for more information on the order of 2:59 operations, if you're interested in learning more. 3:02 Okay, finally, I just need to call each function. 3:05 Remember to call a function, you use the function's name and a set of parentheses. 3:08 Inside the parentheses, I include the arguments, or values, 3:15 that I want to pass to the function. 3:18 In this case, I'm calling the areaRectangle function, and 3:21 passing the width and the height of the rectangle. 3:24 But I also want to print this to the console, so I use the console.log method. 3:27 Now, do you notice something here? 3:38 I'm actually calling two functions. 3:40 The first function, areaRectangle, 3:42 returns a value that's passed to the second function, the log method. 3:44 Now, this is really a common thing in JavaScript, so 3:49 get used to seeing code like this. 3:51 Now, the last three lines are pretty much the same. 3:53 You're just calling different functions with different arguments. 3:56 I'll save this file and preview it in a browser. 3:59 And then I'll open the dev tools, And check out the console. 4:07 There it is. 4:13 I hope you were able to complete this practice successfully. 4:14 If not, why not start over and 4:17 try to write the program without looking at my version? 4:18 Have fun with JavaScript, and I'll see you again soon. 4:21

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