4-1
class Y{
int a,b,y,i;
int sum=0;
public void f()
{
while(i>1){
y=b*(i-1)+a;
sum=sum+y;
i--;
}
System.out.println("等差数列的和为:"+sum);
}
}
public class XIN41{
public static void main(String args[]){
Y y1=new Y();
y1.sum=0;
java.util.Scanner sc =new java.util.Scanner(System.in); System.out.println("请输入首项的值a:");
y1.a =sc.nextInt();
System.out.println("请输入公差的值b:");
y1.b = sc.nextInt();
System.out.println("请输入项数i:"); y1.i = sc.nextInt();
y1.f();
}
}
4-2
class A
{
double a, b;
static double c;
double root1, root2;
boolean boo;
public A(double a, double b, double c) {
this.a = a;
this.b = b;
A.c = c;
if (a != 0)
{
boo = true;
else
{
boo = false;
}
}
public void getRoots()
{
if (boo)
{
System.out.println("是一元次方程");
double disk = b * b - 4 * a * c;
if (disk >= 0)
{
root1 = (-b + Math.sqrt(disk)) / (2 * a);
root2 = (-b - Math.sqrt(disk)) / (2 * a);
System.out.printf("方程的根:%f,%f\n", root1, root2); }
else
{
System.out.printf("方程没有实根\n");
}
else
{
System.out.println("不是一元次方程");
}
}
public void B(double a, double b, double c) {
this.a = a;
this.b = b;
A.c = c;
if (a != 0)
{
boo = true;
}
else
{
boo = false;
}
}
}
public class XIN42
public static void main(String args[ ]) {
A a1 = new A(4, 4, 1);
A a2 = new A(1, 2, 1);
a1.getRoots();
a2.getRoots();
}
}
