Given the length of diagonal ‘d1’ of a rhombus and a side ‘a’, the task is to find the area of that rhombus.
A rhombus is a polygon having 4 equal sides in which both the opposite sides are parallel, and opposite angles are equal.
Examples:
Input: d = 15, a = 10 Output: 99.21567416492215 Input: d = 20, a = 18 Output: 299.3325909419153
Approach:
 Get the diagonal ‘d1’ and side ‘a’ of the rhombus
 We know that,
 But since we don’t know the other diagonal d2, we cannot use this formula yet
 So we first find the second diagonal d2 with the help of d1 and a
 Now we can use the area formula to compute the area of the Rhombus
// C++ program to calculate the area of a rhombus // whose one side and one diagonal is given #include<bits/stdc++.h> using namespace std;
// function to calculate the area of the rhombus double area( double d1, double a)
{ // Second diagonal
double d2 = sqrt (4 * (a * a)  d1 * d1);
// area of rhombus
double area = 0.5 * d1 * d2;
// return the area
return area;
} // Driver code int main()
{ double d = 7.07;
double a = 5;
printf ( "%0.8f" , area(d, a));
} // This code is contributed by Mohit Kumar 
// Java program to calculate the area of a rhombus // whose one side and one diagonal is given class GFG
{ // function to calculate the area of the rhombus
static double area( double d1, double a)
{
// Second diagonal
double d2 = Math.sqrt( 4 * (a * a)  d1 * d1);
// area of rhombus
double area = 0.5 * d1 * d2;
// return the area
return area;
}
// Driver code
public static void main (String[] args)
{
double d = 7.07 ;
double a = 5 ;
System.out.println(area(d, a));
}
} // This code is contributed by AnkitRai01 
# Python program to calculate # the area of a rhombus # whose one side and # one diagonal is given # function to calculate # the area of the rhombus def area(d1, a):
# Second diagonal
d2 = ( 4 * (a * * 2 )  d1 * * 2 ) * * 0.5
# area of rhombus
area = 0.5 * d1 * d2
# return the area
return (area)
# driver code d = 7.07
a = 5
print (area(d, a))

// C# program to calculate the area of a rhombus // whose one side and one diagonal is given using System;
class GFG
{ // function to calculate the area of the rhombus
static double area( double d1, double a)
{
// Second diagonal
double d2 = Math.Sqrt(4 * (a * a)  d1 * d1);
// area of rhombus
double area = 0.5 * d1 * d2;
// return the area
return area;
}
// Driver code
public static void Main (String []args)
{
double d = 7.07;
double a = 5;
Console.WriteLine(area(d, a));
}
} // This code is contributed by Arnab Kundu 
24.999998859949972
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