Creating of math library in C programming language

// header File: math.h
#ifndef MATH_H_INCLUDED
    #define MATH_H_INCLUDED

    struct root{
            float x_1;
            float x_2;
    };
    int square(int x);
    int factorial(int value);
    float convertDegreeToRadius(float degree);
    float sine(float angle);
    float square_root(float x);

    struct root rootsSecondDegreeEquation(float a, float b, float c);
#endif // MATH_H_INCLUDED

// .C file - Functions of library
#include <stdio.h>
#include <stdlib.h>
#include "math.h"

#define PI 3.14159265359

//Calculate the square of a number
int square(int value){
    int i =0, result = 1;
    for(i = 0; i < 2; i++)
        result = result * value;
    return result;
}

int factorial(int value){
    int i, result;
    while (value < 0){
        printf("Invalid value! Insert other value again: ");
        scanf("%d",&value);
    }
    if (value == 1 || value == 0)
        return 1;
    else{
        for(i = 2; i <= value; i++)
            result = result * i;
        return result;
    }
}

float convertDegreeToRadius(float degree){
    float radius = 0;
    radius = (degree * PI)/360;
    return radius;
}

float sine(float angle){
    int i = 0, angle_3 = 1, angle_5 = 1, angle_7 = 1;
    float sine = 0;

    for(i = 0; i < 3; i++)
        angle_3 = angle_3 * angle;

    for(i = 0; i < 5; i++)
        angle_5 = angle_5 * angle;

    for(i = 0; i < 7; i++)
        angle_7 = angle_7 * angle;

    sine = angle - (angle_3/factorial(3)) - (angle_5/factorial(5)) - (angle_7/factorial(7));

    return sine;
}

float square_root(float x){
    int i;
    float recorre = x;

    for (i = 0; i < 10; i++)
          recorre = recorre/2 + x/(2*recorre);

    return recorre;
}

struct root rootsSecondDegreeEquation (float a, float b, float c){

    struct root math;

    float delta = 0;
    delta = (b * b)- (4 * a * c);

    if (delta < 0)
        return math;
    else{
        if (a == 0 && b != 0){
            math.x_1 = c / b;
            return math;
        }else{
            if (delta == 0){
                math.x_1 = (-b) / (2 * a);
                return math;
            }else{
                math.x_1 = ((-b) + square_root(delta)) / (2 * a);
                math.x_2 = ((-b) - square_root(delta)) / (2 * a);

                return math;
            }
        }
    }
}