Function to calculate the side lenght

Question

Hello,

I am new in this topic and need some help. Could possibly anyone write a code to this or maybe give me hint how i could do this? I would appreciate any kind of help.

Problem 1:
Write function to calculate the side length of a equilateral triangle of given area.

Problem 2:
Write a function that will create vector of length N such that the value
of each element is by 3 smaller than the index of the element.

Comments

Looking for help on a Polish forum in English?
At first it would be good if you showed what you have. Write anything you can think of on how to do it.

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How to find the length of the side of an equilateral triangle  

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@MartYNA1111,

stackoverflow is still available and free: D keep using it before it becomes a paid: D or requiring a paid subscription

Answer 1

#include <iostream>
#include <math.h>  //:: pow()
#include <vector> // :: vector<>

using namespace std;

double sideLengthOf_equilateralTriangle( const double&  givenArea_A )        //*****  ( A-1 )
{                                                                            
    const double constValueFormula { 2.0 / pow( 3.0 , ( 1. / 4. ) ) };       //*****  ( A-2 )

    return ( sqrt( givenArea_A ) * constValueFormula );                      //*****  ( A-3 )
}

template< typename T >                           //*****  ( B-1 )     
auto createVector( const int& length_A  )
{
    vector< T > myVector( length_A );            //*****  ( B-2 )   

    int currentValue { -3 };
    for ( auto& elem : myVector )                //*****  ( B-3 )   
    {
        elem = currentValue++;
    }

    return myVector;                             //*****  ( B-4 )   
}


int main()
{
    const double givenArea { 16 * sqrt( 3 ) };
    cout << "lenght = " <<   sideLengthOf_equilateralTriangle( givenArea ) << endl;

    auto myVector { createVector< int >( 10 ) };
    cout << "Vector size ="  << myVector.size() << endl;
   
    cout << "List of elements:" << endl;
    for ( auto& elem : myVector )
    {
        cout << " [ " << elem << " ]  ";
    }

}

/*
    *( A-1 )* ::  Step 1: Simplify the formula to its simplest form.    
    
    *( A-2 )* ::  There is a constant in our mathematical formula that we calculate. 
                  (Speed up functions). It's a good idea to use a function that returns constexpr. 
                  Then the expressions have the form:    constexpr double constValueFormula { 2.0 / otherPowFunction( 3.0 , ( 1. / 4. ) ) };

    *( A-3 )* ::  As a result, we return our mathematical formula.
    
    
    *( B-1 )* ::  Vector type is undefined so i created template. Propably vector<int> is enough. So you can change here vector< int > myVector( length_A ) and remove template;
    *( B-2 )* ::  create vector of length N
    *( B-3 )* ::  assigning values to elements. Each element is by 3 smaller than the index of the element. So first element value = -3. 
    *( B-4 )* ::  Vector filled, so just return. 

*/