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# Calculating the image of an specific value

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HP Prime
Microsoft Windows 10 (64-bit)

Hi, so I've had my HP Prime for about a month now and I'm still learning how it works and I have a question:

Let's say for example that I have a function f(x)=3+5x and I want to know what value of Y does the function take for an specific value of X. Is there a way to calculate it?. Like for example a way to make f(5)=3+5*5 without having to copy and paste the function over and over and replace its values.

That's how I'm currently doing it by the way, just copying and pasting the function and changing its values.

I have other calculator that has a "CALC" button, that allows you to replace the "X's" of any given function by a value of your choice and it shows you the corresponding Y for that value of X.

I was wondering if the HP Prime has something similar, and if it does, where can I find it.

Thanks for reading and have a good evening.

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There are many ways to do this.

Simplest in your case is open the "Function" app. Then define your function in the SYMB screen, (that will be the default that opens when you tap it).

F1=3+5*X

now on the home screen, type F1(5) and you get your result.

You can also use the "define" key which is the shift-template function (the ALPHA D key). That lets you create and name a function for later use, including taking multiple inputs for values. However, you will have to remember to delete it later else eventually you will get many filling space.

You can also go into the CAS screen. Type f(x):=3+5*x  (note the lowercase, uppercase will use your numeric A-Z variables from HOME). This creates an object named "f" that takes as 1 argument, a value called x. x can be any type of value. You are now working in the "symoblic" area, so giving it an input of f(3) returns an exact number, but you could just have easily have done f(3/4) and gotten back 27/4, or f(x^2) and get back 5*x^2+3. To delete the CAS object, run purge(f), or delete it through your memory manager.

So in short, there are many ways to do this. For simplicity, i'd recommend using the Function app for now. There are the fewest potential ways to do something unintended that way.

TW

Although I work for the HP calculator group as a head developer of the HP Prime, the views and opinions I post here are my own.
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Thank you very much for your answer, the first method you told me was exactly what I was looking for! I also discovered that I can go to the "Num" tab, and just type the value of X I want and it will direct me to it's Y value.

I was also wondering about the define function, so that means that I can create ANY function and just say I need a said number of imputs?

Like for example I could create the function: Y-Y1=(Uy/Ux)*(X-X1) and just make it so that I needs the values of Y1, X1, Uy and Ux to create the ecuation for any linear fuction?

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