Вычисление значения функции - C (СИ) (74026)

//Подключение библиотеки стандартного ввода и вывода
#include <stdio.h>
#include <math.h>
double first(double x){
        return (pow(sin(x)*tan(x)),1/2)/10;
}
double second(double x){
    return (pow((x-5)/10),(2))/(log(abs(x)));
}
double third(double x){
    return (x*pow((exp(1)),(pow(x,2)+5))/x);
}
double fourth(double x){
    return sqrt(abs(1+3/2*sqrt(x)+(4/5)*x));
}
int main(void){
    double x;
    int num;
        printf("Set you X value: ");
//Ввод данных
    scanf("%lf",&x);
    printf("Select number of operation (1-4): ");
        scanf("%i",&num);
        switch (num){
            case 1: x = first(x); break;
            case 2: x = second(x); break;
            case 3: x = third(x); break;
            case 4: x = fourth(x); break;
            default: printf("Error: not a valid operation number");
        }
    printf("Result: %3.3lf \n",x);
    return 0;
}

return (pow(sin(x)*tan(x)),1/2)/10;
 return (pow((x-5)/10),(2))/(log(abs(x)));
 return sqrt(abs(1+3/2*sqrt(x)+(4/5)*x));