# Answer to Question #41625 in C++ for Ali

Question #41625

write a program to approximate the integral of a function of one variable. Your program will use the trapezoid rule.

Test your program using the following functions:

Integral of 1/x from 1 to 2

Integral of x2sin(x) from -1 to 1

Integral of x2e2x from 0 to 3

Test your program using the following functions:

Integral of 1/x from 1 to 2

Integral of x2sin(x) from -1 to 1

Integral of x2e2x from 0 to 3

Expert's answer

`#include <stdio.h> `

#include <conio.h>

#include <math.h>

#define f(x) (1/x) //use macros to define the integrand

//#define f(x) ((x)*(x)*sin(x))

//#define f(x) ((x)*(x)*Exp(2*(x))) //uncoment to change integrand

double calcAreaTrap(double a1, double b1){ //function calculates the area of trapezoid of height b1-a1 , and the center line f((a1+b1)/2).

return (b1-a1)*(f(a1)+f(b1))/2;

} // or this function return the approximation value between two end points a1 and b1 , based on the trapezoid method

double calcArea(double A, double B,int N) // this function will return approximation value between two end points,a and b, based on the method specified by flag

{

double buf = 0; // Declaration and initialization of the auxiliary variable tha will be contain approximation value between two points , a and b

double h = (B-A)/N; //Declaration and initialization of the auxiliary variable tha will be contain value of space step , h = b1-a1

//this part will calculate approximation value between two end points

for (int i =0;i<N;i++) {

buf=buf+calcAreaTrap(A+i*h,A+i*h+h);

}

return buf;

}

void OutPut(double Area){ //this function type on the screen area's value

printf("The integral's value is : %f", Area);

}

int main(int argc, char *argv[])

{

OutPut(calcArea(1,3,1000));// by using all define function program will calculate and output approximated value of the integral of the function f(x) tha define in head by macros in interval (0;3) with space step 0.03

getch();

return 0;

}

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