Parabola elements calculator

[sudden mulch]

so, im trying to write a program what would calculate the direction of opening, vertex, y intercept, zeros, and vertex form of the equation. how would I go about doing that?

[restive palm]

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[sudden mulch]

I have the first bit done already.

this is urgent

[robust trail]

What exactly do you want to do?

[manic oar]

The first step would be to figure out how to do each of these things mathematically

Then it'd be a relatively simple task of translating that into Java

[sudden mulch]

true lol

[manic oar]

Once you've done that, if you get stuck writing some specific piece in Java, I think that'd be a more appropriate question for here

If we told you how to do the math we'd just be doing your homework for you

[sudden mulch]

lol, but how do I get user input for specific variables?

[robust trail]

You can use a Scanner, BufferedReader or similar on System.in

[sudden mulch]

thanks, how would I tie System.in to A for example? its been a while so I've forgotten

[robust trail]

For example

try(Scanner scan = new Scanner(System.in)) {
  double a = scan.nextDouble();//read a double and put it in a variable named a
  //do more work here
}

[sudden mulch]

thanks mate

[manic oar]

Alternatively you could pass them as args, which is what I'd do given the choice

[sudden mulch]

apperantly the readDouble() symbol cannot be found

[robust trail]

nextDouble

[sudden mulch]

hmm, never used that method before

[robust trail]

it's if you want to pass input to the application before starting it

[sudden mulch]

there we go, now I just need to do that two more times

[sudden mulch]

I see

[sudden mulch]

ok, so the code can't find symbol A from the double that is defined before that code occurs.

[robust trail]

Variables are case sensitive

and it needs to be in scope

if you define a variable inside a {} block, you can only use it in that block

[sudden mulch]

used uppercase for both

[manic oar]

double a;
try(…) {
   a = ...
}

[sudden mulch]

I defined A wthin the try area

[robust trail]

it's better to write all the code inside the try block here tbh

[robust trail]

Did you also do the same with the code using a?

[manic oar]

Why? I try to keep try blocks as small as possible with only relevant bits

[robust trail]

Also by convention, it's recommended to use camelCase (starting with a lowercase letter) for all variables and methods

[robust trail]

Because it's System.in and you cannot use it once you closed it

[sudden mulch]

I did both with A, and now the scanner can't use A

[robust trail]

I mean technically closing System.in isn't necessary but IMO it's good to get used to it

[sudden mulch]

due to predefinition in main block

[robust trail]

Can you show your code?

[manic oar]

I'd presume he's reading his three things and being done with stdin

[robust trail]

you don't know

[sudden mulch]

here's the updated code so far

[robust trail]

I'd move the code after the try block inside the try block

and you were redeclaring the variable i.e. you'd have two variables named A

try(Scanner scan = new Scanner(System.in)) {
    double a = scan.nextDouble();
    //int parabolaEqualtion = f(x)=A*x^2+B*x+C;
    double dirOfOpening = a;
    if (dirOfOpening < 0) {
        String trueDirOfOpening = "up";
        System.out.println(trueDirOfOpening);
    }
}

[sudden mulch]

that fixed it

now I just need to get B and C defined from user input as well

and then I can do the rest (hopefully)

[robust trail]

Do you know how?

[sudden mulch]

use the same method as A?

[robust trail]

yes

[sudden mulch]

do I need to close the A method?

or is it fine without that?

[robust trail]

?

[sudden mulch]

I mean close the scanner for A

[robust trail]

You should use the same scanner for all inputs

and the try(){} block automatically closes the scanner at the end

[sudden mulch]

cuz I need 3 different values for A B and C to be different

[robust trail]

Note that you don't really need to close System.in (and Scanners on it), that's your choice - but closing is important with some other IO (e.g. files or networking)

[robust trail]

if you run nextDouble 3 times, it will read 3 values one after each other

[sudden mulch]

I see..

[sudden mulch]

ahh, so how can I add a text prompt to nextDouble to make sure the use knows what each is for?

[robust trail]

System.out.println

I assume you are able to use it?

[sudden mulch]

ik how to use system.out.println but I wanted to make sure there wasn't some convaluted method. and im guessing I put one before each double is scanned?

[robust trail]

It should be fine with println

[sudden mulch]

yeah, but does each one go before or after the scan.nextdouble?

[robust trail]

Do you want to first show the user something or get data from the user?

[sudden mulch]

I want to show them the prompt first so that they know what their inputing/what to do

but I also don't want all three going at once

[robust trail]

then execute the corresponding things in that order

[manic oar]

Why is this tagged "recursion" and "maven" lol

[sudden mulch]

recursion???

[sudden mulch]

my bad, should be fixed

[sudden mulch]

so, how do I portray -b in java for the vertex?

[robust trail]

?

[sudden mulch]

cuz I got -75 from A = 10, B = 25

and the formula for a vertex is -b/2a

thats why im asking

[robust trail]

I am not sure what you mean with vertex

[sudden mulch]

im doing a parabola solver

[robust trail]

What exactly are you doing and what's the issue with that?

[robust trail]

so?

[sudden mulch]

I don't think I should be getting -75 from that set

[robust trail]

idk what you mean with solving - Do you want to find roots?

and idk the code you wrote

[sudden mulch]

thats later, im trying to solve the vertex with this point

ill get the code for ya

[robust trail]

I have no idea what you mean with solving a vertex

Do you want to evaluate the function at a specific point?

[robust trail]

I have no idea what you mean with vertex

[sudden mulch]

basically, the vertex is the point at which it intersects with it's line of symmtry

or the point at which a parabola changes direction

so if one side is facing one way, the vertex is the point at which it mirrors itself

[robust trail]

-B/2*A is -(B/2)*A

I think you might want -B/(2*A)

[sudden mulch]

Thanks, hope this works

[sudden mulch]

now im getting -1.25

I should be getting -7ish

what did I do wrong?

[robust trail]

What exactly did you enter? What is the exact code you executed now?

And why should it be -7 instead of e.g. -1.25?

-5/4 seems like the correct value when I view a parabola with a=10, b=25

[sudden mulch]

the point of which a parabola with this set of values mirrors itself is at -7 (values being A=10, B=25, C=8) , the program spit out -1.25 instead. here is my current code which seems to work just fine apart from the vertex calculation

[sudden mulch]

you forgot to add C being 8

[robust trail]

That doesn't change the result

here's with C=8

but I created it before you wrote the thing about C=8

[sudden mulch]

thats where it should be

[robust trail]

that's pretty much -1.25

Do you want the y-value? If so, you'd have to calculate it by applying the function

[sudden mulch]

its -7.8, how is that -1.25????

lol

now that seems a bit rude of me, sorry about that

[sudden mulch]

now that makes sense, Ive forgotten how to do parabola calculations, Im sorry for my oversight

[robust trail]

no problem

[sudden mulch]

wait, how do I do squared in java?

[robust trail]

x*x

or Math.pow(x,2)

[sudden mulch]

ight, and im trying to apply the xVertex value to the original equation but it keeps erroring out, I'll share the code

[robust trail]

^2is not squaring

[sudden mulch]

now that makes sense, but what about the rest of it?

was that the only fix?

[robust trail]

idk, what is the error you are getting?

[sudden mulch]

how do I fix the "possibly lousy conversion from double to int" on the xVertex = vertexformulaX; line?

[sudden mulch]

doing a proper square fixed the first issue

[robust trail]

change the int xVertex to double xVertex;

int means it's for integers i.e. no numbers with a decimal point

double is for floating point numbers

[sudden mulch]

and, why am I getting a new error on the last double line before my final printing line?

[robust trail]

because if you do string concatenation, the result is a String

not a double

double is for floating point numbers, not for text

[sudden mulch]

adding the String header to replace the double header still didn't fix the error

[robust trail]

What's the error?

and idk what you mean with header

[sudden mulch]

cuz im trying to print out the vertex form of the equation but I can't do it straight out with the println function

[robust trail]

idk what the issue is if you don't tell me

btw vertexFormulaY just holds the value, not the whole formula

[sudden mulch]

yeah, so I'm trying to use the string VertexForm to hold the final formula without calculating it so that it can get printed out in the println fuction below it

[robust trail]

What happens?

[sudden mulch]

well, I get a giant block of errors due to the way its formatted presumably

[robust trail]

"X" + + " - "

you have + + there

[sudden mulch]

the two main errors I get are ";" expected and that it's not a statement

[robust trail]

I don't think that's intended

[robust trail]

.

[sudden mulch]

fixed it, but I still get the same errors

I still have to do the roots after I fix this part

[robust trail]

I can't tell you what the issue is without seeing the errors

my guess is unmatching {}

[sudden mulch]

I added the {} brackets but it give me more and new errors

such as "}" expected and ";" expected and not a statement

hmm, and I still need to do the zeros after I get this part done

heres the up to date code

[robust trail]

if you want me to help you, you need to show me the exact errors

[sudden mulch]

I did

[sudden mulch]

right here

its on the String [] VertexForm line

[robust trail]

oh String[] VertexForm = {"y=", + A + "(" + "X" + " - " xVertex + ")" + vertexFormulaY}; is not valid

Do you want a single String?

if yes, just do String VertexForm = "y=" + A + "(" + "X" + " - " xVertex + ")" + vertexFormulaY;

[sudden mulch]

yeah, I want that string to print out the actual one when running

[robust trail]

.

[sudden mulch]

gives me the "";" expected" and "not a statement" errors

[robust trail]

on which line?

[sudden mulch]

the string VertexForm line

[robust trail]

How did you change the line now?

[sudden mulch]

I copy pasted, and replaced the old string line

[robust trail]

ah you forgot a + symbol

before xVertex

[sudden mulch]

that fixed it, I jsut tested the code and somehow the program got -148.25 for the vertex

idk how

[robust trail]

you did vertexFormulaY = A*xVertex*A+B*xVertex+C;

That's A^2 x+Bx+C

[sudden mulch]

so how do I fix it?

[robust trail]

read the line and ask yourself why it does that

[sudden mulch]

ohh wait, the lack of brackets right?

[robust trail]

no

[sudden mulch]

what else could it be?

im honestly at a loss

[robust trail]

What do you want to do with that line?

[sudden mulch]

get the Yvalue of the vertex

[robust trail]

Using the formula for a parabola.

What is the formula for a parabola?

[sudden mulch]

y = Ax^2+Bx+C

[robust trail]

And what's that line doing?

[sudden mulch]

squaring A and adding the rest together?

I think

idk

thought it would work

[robust trail]

Is A squared in this formula?

[sudden mulch]

A*x is

[robust trail]

?

[sudden mulch]

ohh, wait

so I gotta add brackets then

[robust trail]

no

[sudden mulch]

what else could I do?

[robust trail]

What is squared in the formula?

A*x is not what's squared

[sudden mulch]

A is squared? sorry, its been a while

[robust trail]

In the formula for a parabola? No, A shouldn't be squared there

Are you doing that? Yes

Is it done in the formula for parabolas? No

[sudden mulch]

so x is squared then? lol

[robust trail]

yes - in the formula

[sudden mulch]

so I jsut change the 2nd A to an X?

[robust trail]

hm?

[sudden mulch]

so I do xVertex*XVertex?

ranther than XVertex*A?

[sudden mulch]

there we go, that fix it. now all I need to do is the roots

and then im done

idk how to translate it into java code though

[sudden mulch]

would you be willing to help me out with getting the steps translated?

[robust trail]

maybe

[sudden mulch]

maybe?

wdym?

[sudden mulch]

why "maybe"

what would it take for you to help me translate the steps?

[robust trail]

depends on whether I'm sleeping, whether you are showing what exactly you have an issue with, etc

[sudden mulch]

well, I have been showing you what i've been struggling with

and ik you aint asleep rn lol

how would i translate the y=a(x-r)(x-s) into my program?

I think thats the only formula I need for the roots

unless im wrong

[robust trail]

you sue * for the multiplications

or do you mean finding the values r and s?

[sudden mulch]

yeah, cuz I don't fully remember what r and s co-respond to

I just need a working way of getting the roots from A B and C

[robust trail]

the roots which you can get using the abc formula?

[sudden mulch]

and the X and Y values for the vertex if needed

[robust trail]

abc formula?

[sudden mulch]

yeah, how would I use the data given to find it in java?

cuz I found a formula D=B^2-4AC

idk how well it would work in java but if I could get it working, that would be great

cuz I need to display the roots after their calculated

[robust trail]

The abc formula is (-b +- sqrt(b^2-4ac))/2a

[sudden mulch]

and this would allow me to display the roots?

[robust trail]

this is the formula for the roots, yes

one root with +, one root with -

[sudden mulch]

anything specific I need to do to show them?

[robust trail]

if your task requires anything specific

$$
\frac{-b\pm\sqrt{b^2-4ac}}{2a}
$$

[robust trail]

^ that formula

[sudden mulch]

would needing to print both roots count?

[robust trail]

Doesn't seem hard

[sudden mulch]

and the original formula for the roots gives me "")" or ";" expected", "";" expected", and "not a statement"

[robust trail]

because the formula isn't valid Java code

you have to translate it first

[sudden mulch]

how?

[robust trail]

What do you think?

[sudden mulch]

idk lol, im terrible with java

[sudden mulch]

and would I need to use two different formulas?

[robust trail]

yes

[robust trail]

one with +, one with -

[sudden mulch]

ohh, thats what that meant

[robust trail]

and you can calculate square roots in Java with Math.sqrt(PUT_YOUR_RADICANT_HERE)

[sudden mulch]

wait, you mean one with -4ac and one with +4ac right?

[robust trail]

no

there is a +- symbol in the formula

Maybe you should first learn how quadratic equations work before implementing it

[sudden mulch]

oh, wait a minute, now I remember

[sudden mulch]

thanks for all the help dude, its been a few months since i've done anything with parabola's

are these the right ones?

double rootCalculation1 = (-B + Math.sqrt(B * B - 4 * A * C)) / (2 * A);
double rootCalculation2 = (-B - Math.sqrt(B * B - 4 + A * C)) / (2 * A);

[robust trail]

looks about right

[sudden mulch]

cool, thanks for all the help with this