# Geeksforgeeks Solution For " Sum of an AP "

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Problem :- Write a program to print sum of an AP with n terms with first term a and common difference d.

Solution :-

Method 1 :-

#include <iostream>
using namespace std;
int main()
{
int t;
cin>>t;
while(t--)
{
int n,a,b,d,sum=0;
cin>>n;
cin>>a>>d;
sum=(n*((2*a)+((n-1)*d)))/2;
cout<<sum<<endl;
}
return 0;
}

Method 2 :-

#include <iostream>
#include<cstdio>
#include <cmath>
using namespace std;
int main()
{
int t;
cin>>t;
while(t--)
{
int n,a,p,r;
long double sum=0.0;
cin>>n;
cin>>a>>r;
if(r==1){
cout<<a*n<<endl;
continue;
}
p=pow(r,n);
sum=(a*(1-p)/(1-r));
sum/=1.0;
//cout<<sum<<endl;
printf("%Lf\n", sum);

}
return 0;

}

Method 3 :-

#include <stdio.h>
#include <math.h>

double GP(int a, int r, int n)
{
return (a*pow(r,n)-a)/(r-1);
}
int main()
{
int t;
scanf("%d",&t);
while(t--)
{
double N, i, a, r;
scanf("%lf\n",&N);
scanf("%lf %lf",&a,&r);
if(r==1)
{
printf("%lf\n",a*N);
}
else
{
printf("%lf\n", GP(a, r, N));
}
}
return 0;

}

Output:-