41
#include <stdio.h>
#include <conio.h>
 main()
 {int n,i,s=1;
  do {printf("Nhap so nguyen (0<=n<8) : n=");
      scanf("%d",&n);}
  while(n<0||n>=8);
  for (i=0;i<n;i++) s=s*(i+1);
  printf("\n Ta co %d! = %d .",n,s);
  getch();
 }

42
#include <stdio.h>
#include <conio.h>
#include <math.h>
 main()
 {int n,i,kt=0;
  printf("Nhap so nguyen n=");
  scanf("%d",&n);
  if(n<=1) printf("\n %d khong phai so nguyen to.",n);
  else {
  for(i=2;i<=sqrt(n);i++)
     if(n%i==0) {kt++; break;}
  if(kt==0) printf("\n %d la so nguyen to.",n);
  else printf("\n %d khong phai so nguyen to.",n);
     }
  getch();
 }

43
#include <stdio.h>
#include <conio.h>
int main(){
	int n,T;
	do {printf("Nhap vao so nguyen duong n<1000:");
	scanf("%d",&n);}
	while(n<=0||n>=1000);
	T=n-n/10*10+n/10-n/100*10+n/100;
	printf("\n Tong cac chu so cua %d la T=%d.",n,T);
	getch();
	}
 
44
#include <stdio.h>
#include <conio.h>
 main()
 {int a1,b1,a,b,UCLN,BCNN;
  do {printf("Nhap vao 2 so nguyen duong:");
      printf("\n a=");scanf("%d",&a);
      printf("\n b=");scanf("%d",&b);}
  while(a<=0||b<=0);
  a1=a;b1=b;
  while (a!=b)
        {if (a>b) a=a-b;
         else b=b-a;}
  printf("\n %d la UCLN(%d;%d).",a,a1,b1);
  printf("\n %d la BCNN(%d;%d).",a1*b1/a,a1,b1);
  getch();
 }

45
#include <stdio.h>
#include <conio.h>
#include <math.h>
 main()
 {float a,b,c,delta;
  printf("Nhap vao 3 so thuc:");
  printf("\n a=");scanf("%f",&a);
  printf("\n b=");scanf("%f",&b);
  printf("\n c=");scanf("%f",&c);
  if(a<0) {a=-a;b=-b;c=-c;}
  if(a==0) {if(b==0&&c==0) printf("\n Pt vo so nghiem.");
            if(b==0&&c!=0) printf("\n Pt vo nghiem.");
            if(b!=0) printf("\n Pt co nghiem x=%f .",-c/b);}
  else {delta=b*b-4*a*c;
        if(delta==0) printf("\n Pt co nghiem kep x=%f .",-b/2/a);
        if(delta>0) printf("\n Pt co 2 nghiem thuc phan biet: \n x1=%f \n x2=%f .",(-b+sqrt(delta))/2/a,(-b-sqrt(delta))/2/a);
        if(delta<0) printf("\n Pt co 2 nghiem phuc: \n x1=%f+%fi \n x2=%f-%fi .",-b/2/a,sqrt(-delta)/2/a,-b/2/a,sqrt(-delta)/2/a);}
getch();
}

46
#include <stdio.h>
#include <conio.h>
#include <math.h>
 main()
 {int i,n,t;
  float x,S1,S2,S3;
  do {printf("Nhap vao so nguyen duong n=");
      scanf("%d",&n);}
  while(n<=0);
  printf("\n Nhap so thuc x=");
  scanf("%f",&x);
  S1=1;
  for(i=1;i<n+1;i++) S1=S1+pow(x,i);
  printf("\n S1=%f",S1);
  S2=1;
  for(i=1;i<n+1;i++)S2=S2+pow(-x,i);
  printf("\n S2=%f",S2);
  S3=1;t=1;
  for(i=1;i<n+1;i++) {t=t*i;S3=S3+pow(x,i)/t;}
  printf("\n S3=%f",S3);
  getch();
  
  }